I took a closer look. It looks like the way it works is this... It's free to play, however you can buy tokens to give you access to features that are real handy, like queuing up multiple building construction or research goals, instead of having to log in and do them one by one as each completes.
The graphics are fairly simplistic, and look a lot more like Stronghold 1 than Stronghold 2. It's not truly 3D, as it's all simple sprite animation. The initial download is about 13 MB, and then it downloads less than 100 more the first time you run it.
Gameplay is casual. Buildings take time to build, and armies take time to travel. You can log in, queue a few things up (with purchased "premium" tokens, which apparently have a 1-week duration) or otherwise make a few tweaks and send a few commands, and log out. Or spend more time with it to interact with your neighbors, strategize, etc. Some things can be done quickly, and you can sit and watch/interact while it happens, or come back later if you're initiating something that will take longer.
So I'd call it a very casual MMO game.
