I think there are quite a few "okay" malts--ones you'd be perfectly happy to drink, but won't spend any time ruminating over. One I had recently that doesn't stand out in my mind is Tamnavulin. The mother of all "okay" malts is Glenfiddich 12, I think (although I'm sure someone will pounce on me for that). There seem to be quite a lot of these Speyside. It's not really a good position for a malt to aspire to, but to be fair, most of these are probably largely meant for blends and are only incidentally single malts.
On the other hand, the only malts I've had that I thought were entirely unenjoyable were Tobermory, Bowmore, and Fettercairn. And I'm sure those have their fans.