As well as things being interesting in Scotland, with the SNP apparently getting away with arguing "If you want a labour government, you shouldn't vote labour, you should vote SNP", and nobody really challenging that, they will also be interesting in England.
While I don't welcome the rise of UKIP, they've turned a lot of the electoral arithemetic upside down. Seats where the labour party were third behind the Tories and Fibdems are now potentially winnable for them, as the Fibdem vote will collapse and the Tories will lose at least some support to UKIP. So, I think some of their resources may well be re-directed towards seats which were previously written off. Probably to trying to pick up the Fibdem vote.
And I'm not convinced that the Nats' support will stay at 45% levels in the face of a UK-orientated election campaign.