I always cringe a little (a lot) at character customization / inventory management stuff that is nondeterministic. It's kind of like how in the bad old days, wizards had a % chance of failing to learn from a scroll...people don't do that anymore for a real good reason. Knowing that you just failed to get arbitrary loot because of the dice is bad. Seeing the object you /could/ get, and then not getting it because the dice aren't in your favor, seems even worse: it's dangling something very desirable in front of players, then yanking it away sometimes, and often without a choice. Maybe you spent all your effort on it and failed anyway...maybe you know you need to conserve it. I get that there's strategy involved but I'm not so fond of strategy that is that random.
As much as I dislike savescumming, "wow I need that item" seems like a dangerous entry point, a great way to say "well that amazing game-changing item has a 95% chance if I spend all my effort, let me save first", which turns into "well, that 70% chance one is also as good as mine, right? let me save first", which turns into "well I save before 70% chances, maybe I just won't spend my effort on this at all and just reload every time until I get it", and pretty soon you're accustomed to savescumming on everything. Slippery slope but I've been there quite a few times.
Not to mention that playing honestly, and missing a game-changing item because you whiffed a 99% success chance, is a pretty big rage quit inducer all by itself...
Honestly, different people have VERY different approaches to loot and it's not this big of a deal for some people, but it is a really important aspect of games and really subtle changes can have some pretty big side effects. Often, adding things to make a loot system better can have big negatives on the rest of the game! Example, Chrono Trigger and Chrono Cross. Some characters (one out of seven in CT, like three out of dozens and dozens in CC) can steal items from enemies. It's time consuming but they are generally one of a kind, especially from bosses. Lots of players feel like they are obligated to keep one of those members in the party at all times, regardless of all other circumstances--all plot elements and tactical considerations become secondary to "I don't want to miss out on loot", and the game is arguably worse off from it. Not to mention a lot of time wasted on battles just sitting around trying to make the steal roll (and reloading if you kill the critter first by mistake). Yeah...It's not a direct comparison by any means, but item collection often feels like it's separated from the rest of the game, a minigame that you need to win in order to get the most out of the real game. No matter how flavorful and in-character your loot system is, eventually it comes down to "I built this character around looting good equipment, and I got screwed five hours ago, and now the game mechanics are hurting me in a decidedly non-roleplaying fashion".
If you want your ability to loot to be based on your abilities and resources, I really like System Shock 2 (or maybe Iji) as an example. You can hack containers--if you have the skills. You spend resources to do it. Success isn't random: you either have the ability or you don't, and if you spend the resources, you get the prize every time. That lets you plan a lot better the second time through, when the joy of discovery takes a back seat to completionism. They're both fun. And if I know I'm going into a game to try and loot All The Things, I'd have more fun carefully planning out my character and my actions, than I would reloading and reloading and reloading until I can hit all those 20% chances.
Rereading again, I might be going a bit overboard here: So, major important items are not "loot drops", but do they still suffer through the random system? If they do, I don't think it's a good idea. If they don't, and the random items are sufficiently low power that you won't care if you missed one five hours ago (and can't collect them all regardless)...then that's fine, no problems there.