Trainz 12 is pretty decent, with lots of community made locomotives, rolling stock and layouts. A couple of things to be aware of though; first, if you purchase via Steam (Valve), that version of Trainz 12 is suffering from the lack of updates even though Auran/NV3 have updated Trainz 12 several times those updates will not apply to the Steam version of the game. It still works ok, with the major problem being the likelihood of online play is basically nil and getting decent updated content is not possible. Why this is, I've nothing to offer, save that it's a topic brought up with both Auran/Nv3 and Steam fairly consistently.
Secondly, a lot of (most?) the community content gets uploaded to the Auran/Nv3 content service which you get access to. However, be advised you will need to purchase a 'first class ticket' (3 months for $12.99 as example) in order to maximise download speeds and amount of content downloadable in a single 24hr period-- without the FCT you are severely limited.
Highly recommend having a shufti over on the Auran forums. I originally bought the Steamised version of Trainz 2010 and bought a version of Trainz 12 direct download from Auran/Nv3 as the 2010 version had same updating problem. My Auran/Nv3 version is fully up-to-date.
Anyway, some of what I do like about the sim is the amount of really well done community content that is very international; the way the game has a lot of activities that work well (like loading cargo, coal, etc) so there is a nice amount of interactive fun. Layout/route building is fairly easy and there are some decent YouTube videos on 'how to'.
If you are interested in train sims I'd highly recommend Trainsimulator 2012 by RSC (Railsimulator.com) as it's a well done train driving sim with superb graphics. A lot of DLC available for it, lots of community freeware/payware available. Prime focus is on UK rail, however RSC has been busy adding some good North American routes lately. There are some great freeware routes, like C&O Allegheny over at Railworks America site.
Hope that helps a bit
Hussars 20 Minuters Squadron
Trainsimulator 2013, FC2
OFF/RoF/BoBII/SF2 now into FSX