"...we're combining all raid sizes and difficulties into a single lockout. Unlike today, 10- and 25-player modes of a single raid will share the same lockout. You can defeat each raid boss once per week per character. In other words, if you wanted to do both a 10- and 25-person raid in a single week, you’d need to do so on two different characters."
See the whole post here.
Unlike a friend of mine, I don't despise running a 10-man and then running the same version on 25. He's happy about this change. I'm...skeptical about whether this will be a good thing or not.
When I decided to start raiding again my gear was behind my fellow raiders. I took the opportunity to run a few 10-mans in addition to 25 to get caught up. It worked out well. In the new system I can't do something like this. But the rush to get caught up was of my own doing so maybe the adjustment wouldn't be drastic.
In my experience, 10-mans are easier. In two guilds I've been in the 10-man groups cleared instances faster than 25. 10-mans consist of choice picks. That one dpser that who always lingers at the bottom of recount in your 25-man raids? You wouldn't pick him to go to your 10-man.
I foresee 25s being full of players who can't make the cut. Just like 40-mans decreasing to 25 separated the wheat from the chaff, the same will happen here.
In my current guild before this was even announced our 10-man raiders would mention now and then "We've already done it on 10." with a hint of smugness when it came to us doing things on 25.
Which one do I want to raid in? To be honest, 10-man gives you more of a feeling of accomplishment because more is riding on you when you don't have 4-5 others to back you up. By the same token, I'd feel worse about needing to take a break now and then in a smaller group.
Hybrids should feel pretty good about now. Hybrids shine in 10-mans. Ones that can do either of their many roles well are the ones you want in your 10 man. Paladins should be the happiest of all.
A thread over at MMO champion was about making a composition that covered all/most of the buffs and 7 of the 10 were hybrids (Balance and Feral druid, Ret and Prot Pally, Enh and Rest Shaman also Demon and Afflic Warlock , Combat rogue and Disc priest). Of course you're going to end up taking whatever you can get. But don't doubt when someone drops the guild is going to recruit with more specificity.
What this means is players are going to have to get better at what they do. I think players got better when we dropped from 40 to 25. You no longer could hide like when people went afk during raids for long periods of time and just put themselves on auto-follow.
3 hours ago