The graphics were spectacular, running at around 30 FPS on extreme settings on my rig (AMD Phenom II 1045T Hexacore Processor, 8gb RAM, ATI Radeon 5570 graphics card). Looks a lot better than Warhead and performs about the same.
Story was solid. No Half-Life 2, but what the hell. Definitely had some good twists, and the characters were pretty solid. Hargreave is truly memorable, and Prophet's surprising impact really shines. Barclay and Strickland were good supporting characters. Lockhart was a douche, but maybe that was intentional. Gould was okay at best, though his role was surprisingly subdued after the first encounter.
Cinematics were very solid. Unlike Call of Duty where the real-time events are underwhelming and melodramatic, this game has me glued to the screen when I lose control. Also unlike most shooters, where you're always sure that something is going to fly in and save you at the last moment, this game at times had me on the edge of my seat thinking "ok.. this is it.. Alcatraz really is about to die."
The gameplay is incredibly addictive. I love being able to shift between abilities with hotkeys.. towards the end when was squaring off with those 4 cloaked Cephs, I realized I was shifting between stealth, power, and armor like a master, and using the environment like another tool. The strategy necessary to succeed in this game is its greatest achievement. You COULD just run in and gun-out everything, but if you're playing on a proper difficulty level, you better be quick. Conversely, if you try to sneak past everything, you damn well better be careful because with one wrong move you might be faced with a platoon of elite alien bastards and their ridiculous weapons. Balance and strategy are key--this is something that is rarely implemented properly. Simply masterful.
I played through on Normal and unlocked all of the suit powers (mostly thanks to that 20,000 point bonus in the last level). I will be playing through again on the highest difficulty.
Haven't played a lot of MP, seeing as how most of you can kick my ass with your eyes closed. I'll get on that once I finish my second playthrough.
I can understand the complaints about 'linearity', but I think Crytek did an incredibe job with what they envisioned. Bravo.