New classes are usually always fun to play for a season or 2. Since they are usually OP, especially something like warlock that is tied to an expansion, have to make people spend $. Paladin was fun and had a few builds that were fun(hammers, aura, or the brandish one).
Problem with these games(diablo, PoE), for me at least, is they are just not long term games. Its get in, level, get the core items for a build, go run through content for a week or two, getting upgrades and such, but I just cant sit and grind paragon, pit levels, or like in poe's case maps/ubers etc.
At least the couple weeks of most new seasons, especially if it has new class, are always worth it and fun in these games.