Goblin Transmuter is loads of fun, though. In general, that class gets better as you gain more experience with the game, as it rewards reading the map and timing your stuff. Don't underestimate it, though, it can get VERY silly once you know your gods and glyphs and items and stuff. That is unless your doing a Human transmuter because then it's just a rather frontloaded lolstomp, or a pissorf orc transmuter which is an even more front loaded lolstomp. Err, Halfling transmuters are also pretty strightforward, too.
How you get better, or at least one way to get better, is to play a big bunch until you get a feeling about how much you can get away with. For a while there you'll be trying to squeeze every advantage, turn every rock over, fret about every move and so on, but then you'll (likely) notice that you're getting quite a bunch of overkill in the end, so you'll start to play around with the resources you ussually hoard for the boss fight. You'll also (probably) notice that some features let you get away with less thinking than other ones do - this doesn't mean you have to cheeze those, just that you don't have to go mad with sinergy and focus but can play around with stuff because you can kinda eyeball when the boss/es are dead anyway.
Like how the Sorcerer is so strong at spellcasting that you can easily go for a melee fighting dwarven sorcerer and still be a strong spellcaster on top of it with less effort. This then gets you to explore features you wouldn't otherwise explore and single out stuff that are just boring to trounce with. Or it doesn't, because you like the stuff that you can trounce with and you trounce with it and that's all fine and dandy, I suppose.