World of Warcraft: Cataclysm ("Cata" is how I'll abbreviate this from here on, and could Blizzard please think about how people are going to abbreviate their expansion names from here on in?) is a great expansion. People are fired up about the new content, the new trade skill, the art... basically everything. The only problem I see is that instances aren't all that fun. There are some great moments, but most of the effort seems to have gone into two things: gimmicks and fire.
By "gimmicks," I mean the use of non-traditional instance tools. The best example is the first instance I ran: Throne of Tides. This instance has so many gimmicks that it's hard to imagine before you walk in. There are cut scenes, teleporters, a jellyfish elevator, a raid boss you get buffed to kill, mobs that jump out of the walls, etc.
By fire, I'm of course referring to the ground effects that harm players during a fight. Sadly, it's become such a pervasive element of encounters (boss and trash alike) in Cata that your strafing keys will be worn out before the next expansion. This makes a mechanic which was previously a nice way to force players to stay alert into something of a tedious way to make ranged casters less effective. You see, melee attackers like my enhancement shaman just strafe around behind a mob, avoiding fire while they fire off their normal barrage of instant-cast effects. My mage, on the other hand is forever interrupting his fireball casts and having to dump an lower-damage, instant-cast spell instead. My mage just cannot keep up with my shamman for dps throughput, even though they're nominally fairly evenly matched.
So, what should encounter design have brought to the table in Cata? Well, some variety without gimmicks might have been nice, but there have to be enough vanilla fights to establish the norm as well. Let's look at one of the most creative instances in Cata: The Vortex Pinnacle. This instance is entirely built in the clouds, and has some interesting mechanics which aren't just gimmicks. For example, there are trash pulls where the mobs start off in fields that prevent substantial amounts of damage, and you have to pull them out to fight. A nice way to break up the otherwise routine fights without changing the in-combat mechanics if the pull is executed correctly. No one loses dps or has to do anything unusual. There are also some nice fights where the "fire" is much more equitable because it requires that everyone move to a particular side of the boss or that everyone move to a specific location while the boss does some large AoE effect. However, the majority of the trash pulls are of the sort one would expect and the boss abilities don't get too gimmicky.
The only other thing that really feels wrong in Cata is the speed-bump at the start when WotLK and Cata dungeons are viewed as a continuum from level 70 to 85. That is, there is such a radical rise in gear ilevel between the ilevel 187 normal-mode drops in level 80 WotLK dungeons to the ilevel 308 normal-mode drops in the first normal-mode dungeons in Cata that there's no way to avoid some very disappointed players who try to level exclusively in instances from the 70s to 85. To counter this, it would have been nice to see Blizzard change the ilevel of some of the WotLK normal-mode gear (perhaps scaling it all up to the ilevel of the ICC 5-man instances -- at ilevel 219, this would still present a big step between dungeons, but might have softened the blow). Granted, a little questing quickly resolves the issue, but that won't prevent many players from going in cold and feeling like they're of no use in early Cata dungeons.
In general, I think the instance design in Cata shows that Blizzard isn't just trying to pump out the same old thing over and over and that's good, but they may have become slightly carried away in Cata with making instances "special".