To me, on some maps the big servers work alright, but there aren't that many, and none are specifically designed for it. Plus, I have experienced the lag warping a dozen times or more on the big servers, and not at all on smaller servers. The problem is that the larger player limit should have been released with a more comprehensive patch, complete with maps designed for that game play, perhaps new objectives that take into account a larger player base, new vehicles, etc. Sure, that's asking for a lot, but it just makes sense, and really, we wouldn't be complaining would we? No, because we wouldn't need to know that 50 player servers were possible until they released the patch.
As an example of how 50 players can ruin a game. Just last night I hopped into a 50 player server doing Kaukasus. Now, that can be a pretty enclosed map with just 28 or 30 people, but add 20 more? It completely screwed with game play. The Germans couldn't even get out of Backroute the whole entire game. Was it because they sucked? No, it was a pub, they tend to even themselves out unless there is heavy team stacking(there wasn't). The culprit my friends, was the sheer amount of firepower they had to wade through to get to the objective. It didn't matter that they had the same player advantage. There were 10 extra russian players tossing grenades and bullets into that relatively small funnel, and the Shephard's hut area was a chaotic mess too. Think about that, 10 extra russians=20 extra grenades, and a few hundred extra bullets tearing down into those two relatively small spaces. That is overkill, and it was. It didn't matter if the Germans managed to go on a good run and kill 6 Russkies(a major blow in a normal game), because the next spawn wave(5 seconds away), would spawn a dozen or more guys to take their place with fresh grenades.
Another thing I've noticed is that with a larger player base, there are more kills/deaths, however you want to look at it, and some maps are suffering on a reinforcements standpoint. I've seen reinforcements depleted with 5 minutes to go in a game on the 50 player servers, with each team killing at a normal rate, noting fancy. Especially Leningrad. On smaller servers it comes down to objectives, on larger servers it comes down to reinforcements and inevitably ends in a mop up situation for the Germans. Now, some games were made exciting as hell because of this(holding the bridge with a handful of guys for the last minutes), and some were made to be ridiculous(one guy left hiding as four minutes tick down, and the Germans had only taken the first objective).
These are just things I've noticed with the big servers. It isn't so much that it is a bad idea, but it sure could have been implemented better. So many maps reek of Half-Life 2

eathmatch or some other similar game(not saying that's a bad game, but it is not RO).
Off the top of my head, the worst maps I've played with the 50 player limit are: Danzig(too small of an urban environment, reminds me of a deathmatch map with 50 players), StalingradKessel(Almost the same as Danzig, but a bit better, because there are some areas with room to breathe), Arad, Leningrad(Reinforcements,sometimes), Kaukasus(Backroute of death), Basovka(too small, maybe if it were the old Ponyri), and some of the custom maps I am blanking on but you get the picture.