As was the case with the Lib Dems, UKIP can promise things they can't deliver. I'm all for the flat tax rate they suggest, but it will never happen. Even if they are elected, it would be political suicide, just look at all the grief the Tories get for reducing the top rate of tax to 45p.
Sadly for every person who tries to convince me UKIP isn't a one issue party, the only time I ever see Nigel Farage he only talks about Europe. No matter what the subject, he will always mention Europe. Always. In fact, I don't think I've ever heard him really mention much at all that isn't Europe related, apart from being anti gay marriage.
Lastly, it's unfair for parties to attack the Tories (and Lib Dems) for their actions in government. They are governing in coalition, neither is doing what they would do if they were solely in power.