For starters: Zelda. The greatest franchise ever. Constant quality from this. Every Zelda game as been massively fun. Every time one is announced I can't wait and they never have disappointed me. Except with no 2. But hell even Mario 2 sucked, the two easiest formulas in the world they manage to somehow muck it up. Zelda 2 would have been a great game, if only it didn't have Zelda on the cover. (I would like to point out that Twilight Princess is officially the highest selling launch title for any system since Mario 64.
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Mario. Yeah everyone main Mario title has been amazingly fun. From the original to the insanely different no 2, to the brilliance that was 3. Not to mention the SNES' greatest achievement Super Mario World. But it didn't stop there Mario 64 took Mario into a whole new dimensions and goes down as one of the greatest games of all time. Even the HUGELY underrated Mario Sunshine was fantastic.
Ninja Gaiden: Ever since the NES I have loved these game, and they're rebirth onto the X-box was no different. Great titles. Nuf said.
Super Smash Bro.s: Only recently got into these, very fun games. Great with friends. I eagerly await the next edition.
GTA: 1 2, and London were pretty shitty. But 3 and beyond have been stellar. Huge games. 3 was fun because it was the first time I could explore a world this large. Vice City was good because you could make an empire. 5 was amazing because of the "Sims" aspect. I like the way this series is shaping up.
God of War: Period.
Knights of the Old Republic: one of the only good Star Wars games.
Bomber Man: It's fuckng Bomber man. C'mon.
there are probably more, but I can't think of them... maybe later.