DISCLAIMER: I've tried these games for at least an hour if not more, so kinda cheating on this, but 5 mins just isn't enough time to test the waters imo.
Elder Scrolls Oblivion: I had just played halfway through fallout3 and I couldn't shake the impression I was playing a crappier medievil version of it.
Started off on a horrible impression with the character creation, and it just went downhill from there. Complete lack of immersion (for a whole variety of reasons) killed this game for me and any interest I might have for this world.
And I'm a +1 to what a few others have said:
Portal: Hyped up beyond measure, it didn't help that I watched a playthrough of it some time ago so knew how it ended (and Glados is but a pale imitation of SHODAN in my eyes) as well as the story.
Really the only part of the game left for me was solving the puzzles on my own, but not being a big puzzle game fan it just didn't catch my fancy.
Half life 2: There's quite a few reasons for this, all of them personal so please don't jump on me for this one ¬¬ Let's just say the final straw was just getting the gravity gun and being separated from Alyx after that tunnel collapse. Gravity gun+robot that could easily clear the way and I was still forced to go the other way? Screw it, I hated the way so much of the game felt forced on me, like I needed to play it ITS way, no more was this evident then the logic of the level design. Rather then trying to find my own way, I was desperately trying to go the way the game wanted/allowed me to go(some people here say they got lost in HL2, i would guess this is the reason why).
Chase scene especially annoyed me for this (even though I did find it thrilling at times ^^), quite a few times I'd slow down and explore to see where the game wanted me to go (giving combine ample time to catch me if they desired, but they didnt and this killed the thrill somewhat when I realize I actually wasn't being chased), not having been given much directions or a vague idea of where I'm heading to until half way in it (and the map didn't really tell me much tbh).
If this was a sandbox game, combine would have caught me a million times already while I was trying to figure out what was the "correct" way to go.
Oh and I hate freeman as a character, the guy has the personality of a cardboard box (and no I'm NOT freeman contrary to what a few would say).
I'm likely going to force myself to continue this game as I payed some money for this one but it's at the very bottom of my playlist.