What is different or better compared to M&B 2?

[Mztah]

Question in the title, please contribute.

[Harold Shiggleton III]

The steam version has a campaign, and different versions of the classic wave defense mode

[Sigi]

Classic had a very small map because of browser limitations, it often meant that the moment a tank enters the map he was already in range of your AT's. Grenades and flammenwerfers were completely OP, artillery was close to unavoidable, structure placements wasn't all that important. Basically everything is better now because the scale is larger.
However, there was no multiple paradrops behind your lines that lead to swift defeat even though you have a good defensive force.

You have more control over your troops, more gear to choose from. This just a direct upgrade in my opinion.