Yeah, I agree the flail is a game changer. But so is the Woodland. The last three games or so have seen a lot of players camping in the woods for us. The major reason is you have a large chance of surviving the Woodland and even if you don't, destiny cards transfer to your next character. Also, once you have a destiny card you will find it is much easier to manage your fate, which further increases your survivability in the Woodland.
In it's own way, I remember the Dungeon being very much a game changer as well, since defeating the Dungeon Lord can get you straight to the top even without a Talisman. In essence, I think any of the boards are going to have a pretty big impact on the game, even though like DomaGB says, some of them are suitable at different times in the game. The greater question would therefore be what flavour most interests a new player.
The two boards that probably change the basic game the least is the Highland and the Dungeon. Particularly the Highland sort of blends in with the main board, having a similar difficulty/reward. Perhaps a slightly higher reward rate for low-level characters actually, what with all those trinkets lying about. So, if you want the basic game but more of it, I'd get the Highland first and then the Dungeon. If you want somewhere to spend all your gold (on flails), get the City and if you want something that changes the game a lot, get the Woodland. Or the Dragon because that really changes the game a lot as well. Be aware that the Dragon is generally considered the least liked expansion even though it certainly has its charms.
As far as the smaller expansions go, they tend to blur together for me. The Reaper stands out because, well, the Reaper suddenly wanders around the board (which is one of the best additions to the game, period!). The Blood Moon, to me, feels a little like the Reaper's freaky cousin but if you're into werewolves and can't get enough NPCs, go for it. The Firelands changes things as well but I have the same experience as DomaGB: I play with everything so the Firelands has yet to make a big impression, being a bit lost in the hundreds of cards.
The two Realms expansions are really good but I can't quite shake the feeling that they are for more advanced play. It's not that they are difficult to play or understand but I suppose they are more subtle.
The remaining small expansions add a lot in terms of characters, spells, endings, etc. But if you are on a budget or timeline, they add less flavour and can therefore perhaps unfairly be picked up last.
Those are my thoughts anyway.
The reaper is bullshiit. Someone can just send his ass to you and then when you roll they can misfortune your roll and guess what you are killed. you can do nothing to stop it. what a fcuking great idea.
Edited by mrvankil