The mission of U4 is to present 4th EDITION D&D rules for use in non-fantasy settings. These include pre-modern settings, contemporary settings, and those that are far flung fantastic and futuristic. U4 is perfectly suited for any of these following campaigns:
Wild west, with or without aliens
U4 has no included setting, allowing you to explore the rules in whatever context you wish. The rules are offered in a general way, not assuming any time period. The equipment lists a wide range of various firearms. Though most are modern, there are quite a few that are retro and futuristic.
The new "Ladder" system which offers more adjustability with character creation. Modify your class with one of seven ladders.
Eleven new classes including sniper, faceman, infiltrator, and the grappler.
New armor including powered combat suits.
New skills & feats.
All new weapons including traditional firearms, rocket launchers, and laser rifles.
Pimp your auto. Purchase vehicles and modify their features.
All new opponents from fanatics to tanks.
The difference in version page count appears to be one of font size and formatting; the OGL version uses a MUCH larger font, but all the info appears to be the same.
Ultramodern4 is presented as an OGL to both support 4th Edition gaming and to reach a larger fan base. The decision was a difficult one, brought on from conversations with fans regarding the insecurity of the economy. Simply put, some people didn't want to spend money on something they might hate. Ultramodern4 is the result of three years of writing, rewriting, and playtesting. We're proud of the system and believe that so passionately, we're willing to let the product speak for itself. Even though the OGL does reference maps, these maps are only available in the full edition (as they cost money to make). We are hoping that this OGL will reach a larger audience which may result in more sales.