Have it, play it, love it... suggest others play it too
http://www.masterofmana.com/

Were I to start listing what it has I'd start with:
Diverse Civs, (even more so)
Significant traits (like master of water giving you the power to cast riches of the sea... when you have enough mana income),
fully realised and separate faith and mana mechanics,
global spells (wall of fire for every city, arcane armour for all your units),
terraforming rituals, (want more kelp? more arid land? to flood the enemy? earthquakes?)
multiple playstyles (zombie hordes? yep. spellswords? yep. green Fae warriors of the summer court? yep.),
improved combat - more utility units with combat auras, direct damage spells and powered up summons... it has a huge amount going for it not even mentioning the AI, which is great and improving. (I look forward and dread the sea related AI changes, you're still safe if you play on Islands map but then you are in any version of civ... although now a mage can water walk a group of attackers over the sea)
Also the team responds quickly on the boads and the updates are always worthy of a few new lengthy games

I do like Rise from erebus, Civ4's other fall from heaven modmoding main development branch... and the SVN updating they've recently changed to gives easy access to the incremental changes they're trying out... although they're a few months behind Sephi and the team in terms of implimentation of their ideas for the magic side of things. Also almost no AI in since they're waiting till after the mechanics are in... still worth watching... If Valk and Sephi could agree on a common lore, mechanics and join forces the world would be doomed to never leave the gigantic games of civ... but I'd rather see both visions realised, in due time than see a poor compromise

I spent some time the other week on it, played through a few games.

To the questions above:

Seemed as stable as base FFH2, at least I never experienced a crash.  But it does have a lot of missing texts in the civopedia and sometimes inaccurate notes that refer to mechanics that have been changed (rare)

Improvements seemed fine, automating workers didn't crash my economy, but until the 1.1 patch capturing cities can nuke you a bit when you suddenly have huge upkeep due to lack of city influence.  A few disciples creating art can help with that now, and to be honest most games I had a pretty big econ so it didn't matter anyways.  I liked not having to worry about city building upkeeps, but I ended up building almost as many land improvements as vanilla, just a bit slower pace so its a bit meh.  The finding new resources if you have the improvement is fun, esp with the world spell that increases chances to find things, but its pretty OP esp for big civs atm.

AI did seem smarter, esp in splitting forces to raid out improvements and starve cities.  I don't play at a super hard level, but I didn't notice anything totally dumb.

Seemed compatible with any map type or generation script.  I only really tried out the Erebus continent though.

I did find it interesting that with the split tech/ magic trees of research as well as the universal resources that you stockpile like stone, etc . .it actually felt a bit more like Elemental in those aspects.  Its still a very different game but I did find it interesting how different teams of thinkers converge on similar ideas as what a good direction for a 4x is.

My biggest issue was just the labyrinthine understanding of different civ mechanics.  I often felt a bit pigeon holed into a certain tech progression in the early game, get ABC to get these special units for your civ or get rolled by the AI . .and on the flip side getting a grasp on some of the later mechanics is made difficult by the layers of changes that aren't necessarily correctly documented, or are just plain missing.  My civ needs to get Alric the ascended to level 15 to win the game?  Great.  Too bad I can't figure out anywhere how to recruit this unit, since it doesn't exist anywhere in the civopedia that I saw, what tech I would need, or anything about it.  Or the Astrikah civ, who seemed interesting, but for the life of me it seems that one of the most basic and important abilities to the civ - souldrink- is missing, or hidden somewhere.  Or the Sidar, who I would think that the creating haunted lands would be a terraforming spell now, but it isn't, and I still don't know why I get creepers that can create them, or why I don't . .etc.  Just those frustrations in a 4x where you would like to plan a strategy but really can't because until you've played the civ for some time you don't know what the little hidden things are or what might be buggy or what the missing link is that the tech help doesn't tell you.

Still in the end its obviously a very extensive and thought out mod, and at current my favorite flavor of FFH / civ4.  I'd probably love it if I had more time to figure out every little nook and cranny of the different civs, and play them multiple times, but as is, its a bit of fun to have.  Still I find myself reaching back for a bit more Elemental now, which isn't such a bad thing.

MoM has improved AI.  I wouldn't call it great, but decent.

The problem with MoM is that I think there's a little too much bloat in the design.  I think Wildmana was in some ways better (the predecessor)

Thanks for all the info.

Since I have crappy internet at the moment, the download is going agonizingly slow.

It looks extremely promising though as I loved FFH2 and this seems to build on it.

evolution from WM, although now a separate species entirely. Sephi and the team (greywarden, tesb and others) from wildmana decided that the changes they wanted were too big for a patch, spent a while playing around with new mechanics (primary and secondary improvements... and a few other concepts that didn't all make it in the original form) they ended up with a full system for global spells and everything... I only decided to try it when I saw the screenshot of the magic research screen and saw the potential and the path they were taking from the base modmod of wildmana.

Anyway, however long the main download takes it isn't wasted. The next patch looks like quite a few improvements but probably doesn't affect enough art or music files to require another full download for a few versions... despite extra spells, more uses for the new resources and things (unless there's a massive amount of retexturing for MAF reductions and such going on just to prove me wrong)

Trying to turn the whole world into a giant ice cube with the Illians.

Pretty impressed so far.

I had a large number of MAFs as well (I play on a 4 year old laptop mostly, only ~1Gb ram) I've been able to play games much further although it helps to play on smaller maps... I managed to play a standard erebus continent* marathon game as the dwarvern golem crafting race with 50% of the land area covered by my culture before the first MAF (i'd wiped out 4 races) and I hope from the next changelog that Sephi is working on reducing some of the artwork load to help with MAFs too...

Still, mostly it's just hundreds of unit stacks while terraforming during large map endgame related memory problems... so smaller maps if it's a big issue. (I did notice less MAFs after cleaning up startup programs, defragging the drive and things... since upgrading the RAM isn't an option for this computer I thought I'd try tweaking it instead)

*erebus continent seems to be a size above what you choose... i think it makes huge maps even bigger... or maybe that's just my impression from the useful land available

Yeah, in both FfH2 or MoM, I mentally think of any erebus map as one size larger and manually double the number of civs (so if I pick "standard" and it gives me 5 civs by default, I think of that as a large map and add 5 more civs in). I appreciate that they were going for a huge, unexplored fantasy world kind of feel, and I enjoy exploring and killing barbarians and such, but I get tired of it after several hundred turns of barbarian killing, expanding, and still having more room to expand without running up against another civ's actual territory. The balance is just a little off by default, but once you realize that you can adjust for it (assuming you're playing a 'custom game,' which you really should be, FfH2 and even moreso MoM are full of interesting game settings you'll want to look at).

On topic, though: Master of Mana is pretty awesome. The new mana/magic research system is worth the price of admission alone, but they've also polished FfH2 in countless little ways that really add up, not to mention a few significant changes to the basic gameplay. I'm tempted to start listing all the little improvements, but honestly.. if you ever enjoyed FfH2, just start downloading, you'll see for yourself. And in general, any fantasy TBS fan would probably enjoy it too, although it might be a little overwhelming at first if you don't have the FfH2 background.

The only thing I can complain about is documentation, the game is full of things that just aren't explained no matter how much you dig through the Civpedia, not to mention a few (not many, but a few) outright incorrect descriptions that seem to be holdovers from FfH2 (i.e. when God King becomes available, the popup still says something about increasing production, which the civic no longer does). This really doesn't help with the learning curve, but once you figure things out (through trial and error, mostly), the game is a lot of fun, the documentation problems are at worst a temporary barrier to enjoyment.