The Geo+ is basically a stock, original Geo, other than having had the ST kit installed from the factory in place of the stock Geo bolt kit. A thumb screw adjuster has also been added to the feed neck. Other than that, it's a Geo.
The Geo2, while obviously still a member of the Geo family, is a newer, different marker, rather than an upgraded Geo.
The new stock bolt kit incorporates the ST kit, but also now has a new Prop section, incorporating a sprung pressure controlled poppet that helps to save air. You have the thumb screw adjuster. You have a new barrel and a new reg. The reg can use LP or HP output air systems without adjustment. It allows you to get full velocity at lower input pressures. It is also fully rebuildable, with a reversible and replaceable reg seat seal, so no need to buy new reg pistons if the seal gets damaged. You have a grip frame with a profile like that of the Ego9's, with the thick to thin frame. You have a board like the Ego10's with the larger, colour adjustable LCD, and the new user interface. The board is also e-portal compatible (though the USB adapter has not been released as of yet). There is now more space between the reg and trigger guard that some people find more comfortable. Last but not least, and in my opinion at any rate, it's a better looking marker.
The Geo+ is an upgraded version of Planets orginal geo it was there attempt to fix issues that Geo+ owners were having. If I were you Id go for a geo2 there much better and with the 2.1 out you can find a Geo2 for pretty cheap. If you are interested in possibly purchasing a Geo2 let me.