Damn terrazine level is impossible on brutal...
This is definitely one of the game's most challenging missions, particularly if you attempt it too early. It's doable, but you're asking for trouble if you don't have siege tanks and vikings unlocked. I think it's worth it, since you want to have those first few Protoss tech bonuses unlocked for the other missions, but definitely you're going to have a fight on your hand for that on the highest difficulties.
The hardest thing about this mission is that most of the attacking Protoss waves aren't built, and instead spawn in spontaneously. This means you can't use your own sense of timing to gauge when the next Protoss attack will come; it's completely arbitrary, and this makes it really easy to get caught offguard. Save often and reload if a group of Protoss appears out of the blue. Secondly, try to take that second resource site early. The terrazine can wait; if you're losing too many units trying to nab it, the Protoss will just steamroll you once their attacking waves show up. This is a really fast-paced mission, so you cannot afford significant casualties.
Overall, I'd say this mission easily makes it into the top 5 for difficulty. Personally I'd rank it at #4 overall, after "All In", "In Utter Darkness", and "Supernova".
Anyways, I digress...
Starcraft II is a great game, but it doesn't break new ground. There's still plenty of time for Blizzard to patch, refine, and expand on the game, but currently I'd say Warcraft III is the better title.