From what I've played so far, Terraria is actually quite comparable to Minecraft. Both have a pretty steep learning curve at the beginning, similar mechanics, and - so far - about the same amount of depth to the combat. Of course, even if I were far enough into Terraria to give you more than just my first impressions, it is, by all accounts, mostly a matter of personal preference.
Mind you, Minecraft has a pretty big modding community for everything from graphics mods to adding whole new blocks, so chances are if you don't find what you're looking for in either of them, Minecraft might be more likely to remedy that.