morolf: I think I never played that final Brood War level, the 8th Zerg mission or so was as far as I got.
Personally I didn't really enjoy WoL's missions that much, you're always under some time limit and there are very few missions where you can build up a varied army composed of multiple unit types and just crush your enemies (admittedly that mission design was fitting for the story since you're playing as Raynor's rebel force which is pretty much always outgunned by their opponents). HotS by contrast had some missions where you can build up vast Zerg armies and just mercilessly steamroll all opposition :-) I enjoyed that, and I thought its story was the strongest of all the parts of SC2 (though others disliked it a lot apparently).
Legacy of the void was really horrible though...I had disliked the way the story was going since WoL (that stupid retcon...so the Overmind was actually a good guy??? wtf), but LotV really killed Starcraft's universe for me, not interested in it anymore.
I know what you mean, that is my one complaint about the actual levels of WoL as well. I love how varied and challenging the levels are, but I would've liked a few more levels where I could just sit back and build a big force at my leisure. So it really excites me to hear that HotS has more levels like that.
Breja: I always hated playing as the Zerg. I'm not sure why, if it was the levels or something about the zerg themselves but I nevergot through the Zerg campaing in the original Starcraft other than by cheating, because I simply hated playing it. I didn't even get Heart of the Storm. I liked Wings of Liberty fine, but it didn't wow me, and after playing it I felt like I'm "done" with Starcraft. Maybe if the Protoss were next I'd pick it up, but I definately didn't feel motivated enough to buy and play a game with nothing but the Zerg :P
Probably there are a few terran/protoss levels mixed into the campaign, just like there are about 4 protoss levels mixed into WoL's campaign.
But yes, I'm not a huge Zerg fan either, though I like them more than the Protoss. It really bugs me in an RTS when I have units that can't be healed in any way. Which was a nice tactic to use with the Zerg when playing against protoss. Using the [url=http://starcraft.wikia.com/wiki/Defiler_(StarCraft)]defiler's[/url] plague ability you can, in effect, permanently halve any protoss unit/structure's health. Ie full shields but only 1 hp.
But overall this is one reason I like Warcraft more. I love playing each of the 4 factions.