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Terra Nova is a fairly abstract game of fence-building. Players try to move their men on the board and fence off as much land for themselves as possible. If the land features just one landscape, it's even better. The game reminds me a lot of Amazons, but there are lots of refinements in this one.
Landscapes and actions
The hexagonal board is divided into eight different landscapes. There's a small thematic element, which goes awry as soon as you realise your men are perfectly capable of walking on water. So, consider this one abstract.
The game begins with a setup phase, when men are placed on the border. Your basic turn is then to move and place a borderstone or two. There's three actions each turn; any combination of moving and placing stones is fine, as long as you start with a move.
In the beginning there are lots of options and choosing what to do can be hard; in the end, the board gets a lot more constricted and the game gets really interesting - the obligatory move makes some nasty forced move situations.
An area is closed when nothing can move inside it and there are at most three landscapes inside. With three, it's one point per hex. With just two landscapes, it's two points per hex and if the area contains only one landscape, it's three points per hex. That way smaller can be better in some situations.
Players can also share points. If one player has a majority inside the area, she takes all the points. In case of a tie, the points are shared. Stealing areas and cooperation come into play with more than two players.
Chaos and tactics in varying decrees
Terra Nova is chaotic and heavily tactical game. No long term planning is possible, except on some very vague level. Reacting to opponents' moves is what you'll be doing, particularly with more than two players. With two, the game is less chaotic and more of a brain-burner.
Terra Nova is a decent little game. However, I didn't enjoy it much. With two, it's just another abstract and not particularly sharp one. With four, it's much too chaotic for my tastes. I suppose the sweet spot is three - I haven't tried and honestly, I don't mind to. While the game is probably better that way, it's still pretty far from interesting.
However, if you don't mind chaos and heavy emphasis on tactical play, Terra Nova can be an interesting little diversion. I wouldn't expect it to appear on anybody's top lists (as I'm writing this, there's just one rating of 9 at the Geek and no 10's, which is quite as expected), but if acquired cheap, Terra Nova should offer enough value for money if you like the idea.