Most enjoyable huh? I'll take that as being a mix of that which had a great initial impact, can be fun for sustained periods/replays, and has stood the test of time.
1. Ninja Gaiden Black
The best action game ever made, brilliant design, well-balanced challenge, and a blast to play. While God of War, Dynasty Warriors, and even Devil May Cry (one of these things is not like the others...spoiler DMC is good) have spawned many clones and passed on their "genes", sadly nobody has copied much of the stupendous elements of this masterpiece. I wish there were tons of (good) Ninja Gaiden clones. Unfortunately, there's really nothing quite like it...well besides Ninja Gaiden 2 (although it's much more....frenetic than it's predecessor. Great game still, just not as polished.).
2. God Hand
Try it, play it, love it. Stylish, fun, and a real treat to pick up and play. It's got some flaws, but overall it has all the addictiveness of a classic arcade beat-em' up bolstered by a lot more depth, variety in enemies, and a massive moveset, which is totally customizable.
3. Baldur's Gate 2
Decline, popamole, yada, yada, yada. It's fun and hits the sweet spot, the right balance between hardcore gaming and ease of play, through design and a lack of certain turn-offs present in other titles. It's certainly not the mechanically best RPG by far, but it is the one I find most enjoyable.
4. Jagged Alliance 2
Certainly the most Codex-approved game on the list; it's accolades need not be rattled off. Generally it's a fun game to play, and with the options it provides, you can set up exactly the game-style you want. Companies today simply don't have the class Sir-Tech did, letting me avoid huge quantities of gun-porn, and silly sci-fi elements with the click of a few boxes.
5. Way of the Samurai
Choices and consequences galore plus the most innovative action-RPG mechanics I've ever seen. It's too bad the second one gutted a lot of the combat mechanics, though the third one is more a return to proper form. It's also funny as all hell to fight off Meiji government armies with a break-dancing, black samurai by your side while you wield a magic wand that summons attack pigeons.
6. X-Com UFO Defense
If only psionics were not stupidly busted, and the "takeover" fleets did not spawn infinitely, this would be a damn near flawless masterpiece. Still, it's electronic crack at times.
7. Super Smash Brothers Melee
This shit is plain fun with friends. I love Street Fighter and Marvel vs Capcom but those simply aren't nearly as enjoyable.
Honorable mentions go out to Fallout 1, Torment, Gauntlet Legends, Streets of Rage, Devil May Cry 3, any Mario platformer, and Donkey Kong Country.
