Wield Oversized Weapon is not amazing. Most feats are not amazing.
Sadly, D&D 3.x is kind of broken, especially at the higher levels. High-level spellcasters (prepared casters especially) can do ludicrous things when given time, information, and enemies who aren't specifically designed to shrug off their powers... and are often able to swing some pretty overpowered cheese even when not given those things. The epic rules just make that worse, as the epic feats that boost already overpowered abilities tend to be even more overpowered.
Further, 3.x feats in general are kind of warped. Some of them are potential system-breakers, while others are basically useless. Finding one or more feats that are just lousy... shouldn't shock you.
Still, sure, let's look at Wield Oversized Weapon in context... specifically, in the context of "you're a melee type who's built to deal damage by swinging weapons, and you have an epic feat to spend" How does it look compared to the other options?
Well... the Epic Feat pickings for a bog-standard warrior (or equivalent) are not great. You can get +1 to hit for everything, you can get +1 to AC, you can get +3 to DR (doesn't stack with armor, but will stack with itself), you can increase a stat by one, you can increase spell resistance by 2 (if you already have spell resistance)... the significant majority of Epic feats that aren't dependent on already having a bunch of magic or other interesting class features are either mild or situational. Getting +2 to hit, stacks with everything is really not that bad by comparison.
...unless you have control over your available magical items. If that's the case, then strongarm bracers (at a price that's petty for you) will give you all the benefit of both Monkey Grip and Oversized Weapon, in one very affordable package. Sure, it means that you need to use your bracers slot... except that you can take Additional Magic Item Space with that Epic Feat you've just opened up (leaving you the original Monkey Grip feat slot to do whatever with), and still have a bracer slot free for whatever you wanted a bracer slot free for.
While there's an argument to be made that one could stack Strongarm Bracers and the two feats, that doesn't even matter, because we can take normal feats with our Epic Feat slots. See, the thing that sinks epic general feats is that there are so few of them. 3.x is crammed to the gills with feats, 90% or more of which aren't worth taking pretty much ever from an optimization standpoint. Compared to the average feat out there, +2 to hit is really quite good... but there are so few epic feats overall that once you trim a few off the sides (say, by ignoring all of the broken Epic Spellcasting feats) it turns out that what you're looking at pretty much are the at-best-mediocre feats, by and large. Compared to the other kinds of feats that you can acquire, +2 to hit is okay, but not really competitive. Worse yet, it's not really even giving you +2 to hit for a feat. After all, realistically, we're only getting the step from medium to large, or maybe the step from large to huge, and it's at the cost of 2 feats. Looking at the weapon size table, at best that's giving you +1d6 damage per hit, and for two feats, at that level, that's kind of pathetic.
So... yeah. First, 3.x doesn't work well at epic levels without (at minimum) a lot of massaging and houserules by the DM (and if you have those, you should be talking with the DM). If you're in a largely non-houseruled epic campaign, then one hopes that you'd have one of the builds that would let you get some actually good stuff our of Epic Feats (...because in general, if you don't have that, your ability to contribute meaningfully is suspect regardless of what you do with said epic feats). If you're in a largely non-houseruled campaign with no interesting powers to buff, then there are better feats to buy. There's a lot of shiny non-epic feats out there, and there are a few gems even in the epics. For example, you could get a lot more mileage out of buying Additional Magic Item Space repeatedly and festooning yourself with expensive and powerful magical items.
In the context of all published feats for fighter-types? Wield Oversized Weapon isn't terrible, for what it does. There are certainly worse out there. In the context of "feats you might actually want to take, given a reasonable selection"? It's pretty bad.