ComputerAndVideoGames.com has dished up a very short review of SpellForce: Breath of Winter, giving the expansion an overall score of 76/100. An excerpt:
The rest, however, works brilliantly. The skirmish-style 'free mode' is as you would expect, but here you can take your experience and items back into the main single-player campaign - even if you're playing co-op. The multiplayer code is tighter as well.
Overall, a good solid expansion - slightly rushed and with some issues still unresolved - but with plenty of magic left in it.