I already own "Sgt. Peppers" so rather than be obvious I thought I'd buy "Magical Mystery Tour" to sample the 2009 Remasters.
I would describe the new version as "clearer" and "sharper" than the original. There is certainly an obvious increased level of awareness of what is going on in the songs.
This is often intensely distracting. The most obvious example is the instrumental "Flying". On the new CD I was acutely aware of when each layer came in. When the guitar comes in it is quite jarring, as is the audible tapping of either Paul or George to keep time. The old version of "Flying" never bothered me, and it is an example of when boosting the clarity of a song can (at least in my ears) reduce it's enjoyment.
"Magical Mystery Tour" was originally mixed in Mono and recorded on four-track. Due to the small number of tracks they often used the same track for multiple instruments (eg. bass and drums on one track).
When later remixed to Stereo, compromises had to be made. These little mixing quirks are part of why I like The Beatles (and bands of similar eras like Simon & Garfunkel). The oddness of mixing the bass and drums in one ear and the vocals in the other adds to the general ahead-of-their-time strangeness of the compositions.
Unfortunately for me, the clarity of the new remasters amplifies the compromises they had to make. The parts of many of the songs feel completely separated, like Ringo and Paul were on one room, while Lennon was on the other side of the world in another. The clarity of each part also amplifies the low quality of the hardware these guys were using.
I've been very negative, but ultimately I liked the remaster... but I think I prefer the 1980s release. In fact, it made me very curious to hear the mono version, which wouldn't suffer from any of the problems I discuss above, but would miss out on the mixing quirks I enjoy.
I suppose all remasters are going to suffer from the same problem, they're competing with more popular and familiar versions of themselves.