I was a big fan of the first game. This one adds some interesting additions, but I think the "click to activate" items start to clutter up the levels rather quickly, and can be a big buggy on the bosses where you have to click on things. The cut-down spell being used to capture buildings is interesting, but I think I preferred clearing an enchanted square to build a tower on to get more mana.
I like the 3rd option for final upgrades, and the captureable buildings with interesting effects (such as lighthouse, tavern) but I don't like the enemy spawning ones as they get you in a catch-22 of build towers to defend, or cut them down to lower the enemy count. The levels with them don't have enough spots to build towers without cutting down forest, which means leveling up cut-down mana cost is the single biggest upgrade.
One strange thing is the Balista has a bigger splash range at level 1 than level 2! Is this on purpose or does the guide lie?