I don't get why people freak out about water levels, they really aren't that bad. There are some non-underwater levels I've played that are WAY WORSE than any underwater level. Also ice levels, those are worse than water levels sometimes.
i like water levels it just depends how it's designed. i like the extra tension added with the oxygen gimick and the strong currents such as in mario's mission and mario gives up but also for it to be fairly difficult mixed with the gimmicks
Depends entirely on how they're designed. Most of what we see is boring and slow-paced levels that have nearly the same layout, but you can create a level that stands out from the average ones if you do it the intended way. I did a few rooms of a level that were centered around the air meter and it turned out to be interesting and entertaining, because you're actually challenged to gain air as rapidly as possible to refrain from drowning.
I personally think Ice levels are much worse...I don't have a problem with Underwater levels though in Mario games I suppose they aren't the most interesting. I guess I just really don't mind the whole swimming to places and avoiding enemies aspect.
It´s quite hard to design interesting underwater levels just useing vanilla resources. But that doesn´t mean custom stuff make water levels more interesting. It can make a underwaterlevel more interesting, but it can make it also worse.
I personally don´t dislike waterlevels per se. I just dislike if there´s a whole underwater world containing 23 exits or something like this. Some underwaterlevels here and there may be a nice alternation to the usual grassland or whatever level.
I like them when they are made right, I think water levels have some good stuff in them if you don't make the same thing that all developers do, like slow and boring and limit the player. A fast water level can be a very fun.
-------------------- Made you look. Now Breath Manualy.
As you can see, the thing these levels do right is uniqueness and creative level design. Much like regular levels, water levels can be either bad or good depending on the amount of thought the creator puts in. Of course, a flat swimming level with dodging fish is obviously gonna be worse than a flat level with jumping over koopas. Water levels move slowly so that's why it sometimes annoys people who don't like the mechanic. A good way to speed up the slowness is include fast paced segments, swimming upwards in vertical levels (since you swim up much faster), fast tides (see municipal swimming), or including throw blocks everywhere (see crystal reef garden).
I prefer levels with tides or not a fully-flooded speed, principally because it's hard to see interesting water levels that play innovative and not your typical fish-dodging game. I have to admit that when it comes to designing them, I can't.