I haven't seen all that much difference in enemies, levels, music, story (what little there is), bosses, characters, and over all gameplay since it started.
You haven't seen much difference in the enemies, levels, music, bosses or gameplay? You've obviously never even touched Mario Galaxy then, or you played a single level
once and are basing your entire opinion on that one brief occurrence.
Your not indifferent of the games(like you claim to be), you're actively biased against them; that's why everyone lashes back at you when you go around continually posting crap like you have been. I don't care about MGS games, they're fun but they never drive me to actually get them; that's indifference. You, however, hate Mario pretty much for the sole reason that it's Mario; while saying you enjoy games that are just as/even more shallow as you claim Mario to be.
Since I haven't played much of Resistance and none of assassin's creed, I'll have to compare Oblivion to Mario Galaxy.
Levels:
Oblivion - only has 4 level types, in a cave, in a dungeon, in oblivion, and outside. They all look identical(outside has a palette swap between snow, grass and dirt, but it still looks the same), there's absolutely no variety between the the levels at all.
Galaxy - over 40 worlds, and maybe 10-15 of them just have similar motif's, but still have wildly different layouts.
Enemies:
Oblivion - maybe 12 in the entire game and you can see all of them early on if you level yourself quickly.
Galaxy - lot of enemies, some are ubiquitous, like the goomba, the koopa troopa, the Boo; but most worlds have unique enemies. Each level has different enemies(or at least real variations on the old ones, not just palette swaps), so you're constantly seeing new ones as you progress.
Story:
Oblivion - story is for all intents and purposes non-existent, since they give you no incentive whatsoever to actually work on it; it seems like more of an afterthought than any real driving force throughout the game.
Galaxy - story is simplistic, as all of the Mario games are(except for the RPG's), but those games are primarily about the game play and never tried to tout a good story.
Bosses
Oblivion - bosses are killed almost exactly the same way each time, the only difference would be if you prefer magic, melee or ranged combat. You'd still find one method of killing that works well and use that for the rest of the game.
Galaxy - a different strategy for each boss, the only exception being the two you fight more than once(Bowser and Dino Piranha).
Music
Oblivion - Honestly I can't remember that there even was music in the game, it was that un-noteworthy.
Galaxy - Nothing to throw on your iPod, but definitely more noticeable. The remakes of the classic music is awesome for anyone who's played the classic games.
Gameplay
Oblivion - As I said before, pretty much the same throughout the game; you find one method of doing things and you stick with it. The only real variance would be if you play through it again. You can do anything, but that gets boring pretty quick when you don't have any incentive to do anything.
Galaxy - Wildly different gameplay on a lot of the worlds. The different transformations you can pick up give you entirely different abilities; the different travel methods are completely different than the normal platforming.
I liked oblivion when I first got it, but primarily because of the modding community. The game by itself is pretty boring, the mods are what gives it some life; but even those get boring after a short while.
You don't like it because it says Mario on the cover; just accept it, admit it, and stay away from Mario-centric discussions. You're offering nothing of any worth to them, just making yourself look foolish.