I was fortunate enough to try Niagara with a great gaming group. I played with Mike, Donna, and John.
I was the only new player, and it took Mike only 5 minutes to explain the rules to me. (One reason why many Euro games are great).
The board setup was very interesting, as the clear plastic disks were set to carry the boats down the river toward the falls. The "gems" each player collects look good too.
On my first turn, I didn't "optimize" like the other players did, so I was a bit behind from the get-go. Mike, Donna, and John all grabbed the nearby purple gems. After the current moved us, I was able to grab an amber gem, so I stayed close at least.
The river was generally calm and predictable throughout the early rounds. Just about everyone used high "paddle" values early, and low paddle values late, and the weather stayed at "zero", so navigation wasn't too tricky. There wasn't much gem stealing, as most had full boats at all times.
The closer white and purple gems were distributed among us, so that nobody could get 4 of them to win, so people had to look further downriver.
Mike and John jumped out to quick leads with 4-5 gems each. Donna and I had 3-4, but they were a smattering of different colors.
The river got wild at +2, as people decided it's more fun if the river is racing. From this point, it was mainly a struggle to keep boats from going over the falls. It's tough to play a "cloud" paddle to tone down the current when you've got boats on the river you're trying to save!
Through stealing, Mike got 6 gems, and John got 6 collected as well. At that point, they didn't care so much about losing one boat, and they each did lose one. (The river was raging at +2 for awhile) Donna and I concentrated on getting one gem of each color back (our boats spent a lot of time near the pink and blue gems near the falls, because of the rushing river).
The river calmed down as our paddles were exhausted, so Mike and John were able to get back to shore with their 7th jewels on the same turn, right after our paddles were replenished. I had my last gem needed to win (with all five gem colors) on my boat one away from the shore when it ended! Donna had had tougher luck with losing a boat to the falls, and getting robbed in the lategoing, so she wasn't as close behind.
Mike and John drew with 7 gems each. Donna and I each had 5 gems. After battling the fast river, it felt like an accomplishment just getting to the game end without being too far behind.
It was definitely a fun game to try. I'm not sure if repeated playings would make it more interesting or not for me. The game play and the decision making didn't seem all that exciting. This game is all about the river. Niagara made it feel like I was really battling the river-- sometimes frustrating and a little nervewracking, but fun.
On my first turn, I didn't "optimize" like the other players did, so I was a bit behind from the get-go. Mike, Donna, and John all grabbed the nearby purple gems.
It is usually a good idea to play the large numbers when you are further down the river. See another thread here for some tactical tips from Alan.