I can't be much help on the building of coasters since I haven't taken that on yet, but I knew someone that picked up on it immediately with basically no experience. I just simply love riding other peoples coasters and have found some incredible works of art out there in No Limits land.
Things I like to do on No Limits. A simple keystroke will allow you to easily change seats while riding, change cars (it defaults to the front seat but you can do the back or any car). You can also do fly overs and view the coaster in operation at any birdseye angle you want. Sometimes I will view the train as if I were sticking my head up between the track rails and watch the car zoom over my head. You can also take screenshots like you can on RCT3.
With the upcoming NL2, there will be a walking mode which will allow you to walk around the coaster. Complete with walking sound effects. There is a sample video of this in action on the website. It is incredibly life-like. The landscape effects are pretty good now but supposedly going to be even better with the new version.
I have only seen RCT3 in action briefly and in my opinion, No Limits blows it away. I am sure some of you would beg to differ and that is fine. Just my opinion.
If I were you I would download the free
DEMO from the NL website. Link is on the bottom right.