I like it, but it's a good thing it was free. It wasn't exactly an upgrade on the level of being worth paying for. On the whole, it barely even feels like anything new, and I'm a huge Apple fan. Messages works better, which you can use to iMessage to iPhones and iPads, I love that. The new maps app is nice, I like being able to look up directions then send it to my iPhone. Supposedly there are features that help prolong battery life as well, but that's difficult to tell. I haven't had any problems with it though (like freezing or errors etc) some people are saying there are some issues with the Mail app I think, if you use Gmail, but then again most Gmail users probably use it in a browser anyway. Anyway, I'd recommend the upgrade since it's free, but don't expect too much out of it.
What OSX are you running now? If it's Lion or Mountain Lion at least, I would bet all software you have now will work. I didn't have any issues with any Adobe software, but I can't vouch for much else. Good luck!