I haven't made levels in, well, years now, but I seemed to be obsessed with climbers, probably because they are generally under-utilized and there are tons of puzzles you can make using them. The fact that making a lemming a climber can be both a good and bad thing makes their dynamics really interesting. I try to mix it up, although I do have several levels that involve much building. Really, I don't have a problem with building. The problem is the "hero lemming" concept, with one lemming doing everything (read: building!), paving a way for the others.
Short and sweet levels are the best! There's a time and a place for the longer, more involved (time-wise) levels, but they should be the exception, rather than norm.
Short and sweet levels are the best! There's a time and a place for the longer, more involved (time-wise) levels, but they should be the exception, rather than norm.