The Debut III is a very good deck for the money. I know several people who've owned them, and every one of them upgraded rather quickly. It's not because it's a bad deck, it's just that the tonearm doesn't really do well with a better cartridge. The Xperssion has a far better tonearm that'll handle a few steps up the ladder.
But it must be said that the Xpression's stock Sumiko Oyster cart is garbage. Plan on scrapping it almost immediately for something else. The dealer I bought my Dynavector cart literally thought it was broken when I brought the deck in. After putting the cart under a microscope, he said "this cartridge isn't shot, it just really sucks!" That wasn't a sales pitch, as he's earned my trust.
There are some excellent carts out there that won't cost an arm and a leg. Ortofon and Goldring come to mind. Grados do to, but they have hum issues with Pro-Ject's and a few others in my experience.
Sorry if that's getting side tracked. In a nutshell, if you're considering an Xperssion, budget an extra $100 - $150 for a suitable cart. But again, the Xpression easily justifies the extra cost over the Debut.
The Music Hall 2.2 is an interesting deck that's a bit cheaper and comes with a far better stock cartridge than the Xperssion. I know a few people who've been happy with the 2.2 for quite a while.