GoWIII is easily the best game in the series. Best graphics, best combat and easily the best and most memorable bosses. EVERY single boss fight was epic (except the last (3rd) battle with Zeus).
The fact there are nearly no puzzles in the game is also nice. GoWI and GoWII are games that I found incredibly boring on my second playthrough (via the remastered PS3 edition). It just didn't have the same impact on me as I originally played the game. I felt I had to force myself to complete some sections of GoW and GoW II. There is no way I'll ever replay those games again. They're great games when you play them once, but doing all the puzzles again is so boring.
GoWIII on the other hand feels great every time I play it. I agree the game lacks environmental variety and but personally I think that is the only downside of this game. Everything else has been improved. The scale, the set pieces, the music (especially when you are fighting Hercules. That was the most epic fight in any video game I played!), the combat and of course, the amazing graphics, were all top notch. I loved the motion blur. Makes it the best looking console game I've played.
After seeing Clash Of The Titans I honestly crave more God Of War. I really hope they make another game.
But seriously, WTF at the lack of costumes. I want a mode where I can play with all my weapons, magic and health upgrades now I've platinumed the game. No New Game+ really does suck. And eurgh @ unskippable cutscenes. Who the hell thought this was a good idea?