The Riftbreaker is pretty good and has a free demo.

[shortylickens]

The Riftbreaker on Steam

The Riftbreaker™ is a base-building, survival game with Action-RPG elements. You are an elite scientist/commando inside an advanced Mecha-Suit capable of dimensional rift travel. Hack & slash countless enemies. Build up your base, collect samples and research new inventions to survive.

store.steampowered.com

No full version yet. The demo is short but good.
I recommend playing it once. Should take you between 10 and 25 minutes depending on how awesome you are.

 

[JTsyo]

I saw one of the dev play session and seems to be the right mix of base building/ TD and RPG. It's on my watchlist.