Get a taste for u-he’s soft synths by checking out the free TyrellN6. The interface is straightforward and it sounds great. I’ve also been having a lot of fun with ACE (Any Cable Everywhere), which is more full-featured than TyrellN6 but still very accessible in terms of UI and cost.
Here’s a look at TyrellN6 in Bitwig Studio.
u-he has another free, and more experimental, synth called the Triple Cheese. I haven’t tried it yet but it’s installed and ready to go.
For more free synths have a look at this post over at musicradar.