Good replies and discussion here, Youngblood. Welcome to EpicSki!
As an instructor, I've been an Elan fan and rep for about 15 years now, so you should consider that I may be a little biased here.
That said, the Mantis 12 is an excellent all-mountain ski for a strong skier, with enough ski performance to work well on-piste too. The M10 is a great ski too--same shape, but considerably softer. I love it in soft snow, but I thought the 2002-3 version of the M10, was a little soft for high performance on harder conditions. Next year's M10 incorporates a layer of metal in the mid-section, which should give it substantially more "beef" on piste than the metal-free 2002-3 version.
Both the M10 and M12 will come in two versions next season--a "traditional" version, and the new "Fusion" system that incorporates a special Marker binding mounted on floating tracks, essentially INSIDE the ski. This system provides a very direct connection to the edges, and floats to allow the ski to flex completely freely beneath the boot and binding. The two skis have considerably different feels--some love the new Fusion system, others prefer the feel of the traditional version.
And there's another new ski that you may be interested in, in the Elan line. The "S" line--which also includes an S10 and a higher-performance, stiffer S12. Also a great all-mountain ski, the S-series is slightly narrower waisted with a little more sidecut than the M-series, so it performs even better on-piste (while perhaps sacrificing a LITTLE bit of "float" in the soft and deep). It, too, will come in standard and "Fusion" versions.
I skied the Mantis 10 this season in 176cm (I am just over 6' and light, and tend to ski fast). I got a pair of next year's S12's this spring in 168cm, and fell instantly in love with them. They're pretty beefy, so they're not particularly forgiving off piste, but it may be the best all-around ski I've ever skied.
If you really want an off-piste performer, take a look at the Mantis 777. It is wider and considerably softer than the M12 and M10, with a hand-built vertical sidewall laminated construction (like top race skis). It is a surprising performer on groomed snow, but truly phenomenal when it gets soft.
Both the Mantis and the S fall into the category of skis that most major manufacturers do pretty well. There are lots of great all-around skis out there these days! But at least to me, nothing else feels quite like an Elan.
More information than you probably needed....