ill try to type what i feel is the issue about the dw tier on both PO and smogon servers, without using words like stupid or broken...
for PO, aka dw with swift swim and no team preview, the problem with the metagame is that it's very, very difficult to consistently win all matches on the ladder. there are simply so many threats to be considered that it's super difficult to build well-rounded teams that can cover everything, and when this happens, most people tend to use either hyper offense or outright stalling. these strategies can go far and can be full of surprises, but neither can really cut it as far as winning consistently goes. it is possible, though, because i've seen high ladder players stay high on the ladder. i think because the meta is so young, most players are still very experimental, and eventually it will be more centralized to things like politoed or whatever.
here are random threats i run into that are already very good without team preview, but are buffed by the surprise factor of no team preview:
- espeon. never guarantees hazard/status setup
- scarf ditto. stops hyper offense teams in their tracks by using the opponent's setup against them.
- zoroark. not a great pokemon, but the mindgame of having him out is buffed without preview.
- absorbers. heatran, zapdos, jellicent, etc, the occasional sap sippers, even poison types absorbing tspikes. this type of selective defending and the increased variety of attackers makes it very difficult for any type of offensive strategy to cover everything. even great rain teams can be stopped cold by a well-placed toxicroak.
- po server in particular: rain + swim. it's really good and building a team in this tier on po server is just something entirely different when you have to attempt to build teams that can beat swift swimmers. doable though
i can see this metagame getting better in the future, once people are more and more aware of what are REAL threats and what's just getting hyped up. u-turn was extremely good in gen iv, so i can imagine volt switch being quite good in the future too. idk though, predicting metagames is difficult. however, i just know that the dw tier without preview is extremely different from what it is with team preview.
dwou, team preview on smogon, no rain+swim:
having the ability to scout beforehand allows more strategizing to be done before the match. lots of people bag on this because it takes away the intelligence involved with scouting... however i just think the scouting mindgames are transferred to lead-choosing mindgames and executing strategies that have been altered in preparation for opposing threats. the only reason i made it so far on dwou on smogon was because i played very intelligently for a good week or so by really really focusing on choosing my lead and establishing offensive momentum.
anyway, about the tier. like i said, threats can be prepared for. i'd admit lots of my pokemon weren't godly, but they had the tools to bust through lots of strategies. for example, i used nasty plot ninetales and qdance/hp ice lilligant to perform sweeps that my other much more common sweepers (loom, ken, cloyster) would not have been able to do. i think this tier might be more balanced and allows for more diversity because even the strongest threats can be strategically prepared for before the match even starts. there are MANY things you can know beforehand just by looking at the other person's team.
when they're gonna spore, what they're gonna switch out, what strategy they could possibly implement, etc. i cant say much about individual pokemon in this meta apart from weather inducers because besides them, the metagame is very diverse.
and thats what pretty much defines the dw ou metagame right now. this is what we call balance via power creep. the only reason marvel vs capcom 3 is balanced is because nearly every character can pull 100% combos. it's the same with pokemon bw. sooo many pokemon are out there that can sweep entire teams that it seems almost impossible to create just one team that can defeat all of them. we can complain about one or two pokemon, but maybe our team just isn't prepared to beat them.
so rather than talking about each pokemon's strengths in theorymon, it can also be productive to talk about each pokemon's relevant weaknesses in the tested metagames.
some examples...
beating ditto: a lot of times the best way to beat ditto is just to prevent it from coming out, and predicting it when it does. ditto's always scarfed so it's easy to know what it'll do when it comes out. just make sure that you have a sweeper out that can't kill itself (my hp ice lilligant says hi to hp dark ditto). or don't setup when you know the other guy who has ditto can use your +2 atk against you.
beating espeon: just don't use reflectable stuff at inopportune times. you can set up rocks against a team with espeon as long as you don't do it on the obvious turn. of course, this is impossible to do without team preview

same with ditto (which is why ditto and espy are godlike on PO)
beating chandelure: revenge. scarf chandelure is made to do one thing and one thing really really well... get FREE KILLS. however its hard ttar weakness, weakness to all hazards, weakness to sucker punch/aqua jet... things like that make it not very hard to whittle down in the long run. if a team isn't prepared for it, that's the player's fault. it's nowhere near centralizing.
beating... conkeldurr: don't status it and attack its spdef in an attempt to ohko.
etc
etc
we can talk about sooooo many pokemon and it's just a matter of knowing how to beat them. also, i think defensive/offensive/balanced CORES are more important than talking about individual pokemon. talking about individual pokemon usually leads to complaints.
now to be a little more subjective...
yes i agree that rain + swim ban is lame LOL.
here's my opinion about dw abilities:
i wanna make a conjecture that....... game freak made them to allow more ordinary pokemon to compete in an environment with ubers included. their abilities certainly do bring lots of pokemon up to par with them. techloom? cloyster? chandelure? espeon? ditto? there are lots of pokemon now that can fight ubers.... ubers! many of whom got very lame dw abilities, or none at all.
oops cloyster doesn't even need its dw ability to tap.
edit: ^^^wow my post was much longer than i thought. tl;dr my views on dream world are not complaints. yay you guys get to hear the chokchokz kinda sorta not sound spammy^^^