I was really missing Panzer General series and its operational level simulation. This game delivered but also gave me something new. The main innovation, suppy lines, has a big effect. One must think about encirclement and weak points instead of wiping out every unit in one's path. It's also important not to leave your supply lines exposed as having them disrupted even once can mean the difference between victory and defeat.
The mechanics are fairly easy to master and the game can tell you how many units you can expect to destroy/lose in any given encounter. There are many interactions to consider (terrain, weather, entrenchment) and since its an operational level game you can be winning individual shootouts yet lose the big battle because you are acting too carefully. The game takes about 20 hours to fully master but provides replay value as you can try to win every battle with a brilliant victory or just try a slightly different approach.
Unlike PG you can finish each scenario in one sitting. The size of the maps is pretty manageable. There's no such diversity of units as in that game but I didn't really miss it. Ultimately the most interesting thing about the game is making decisions of how many units to commit, where and for how long and doing it all without outrunning your supply lines, often this requires coordination between units.
My two complaints are: the AI is a little weak, enough to provide a challenge but not enough to really surprise you and often committing foolish errors; the other is that battles can only be played in a pretty strict sequence. So if you finish a campaign and want to replay a battle from near the beginning, the later battles will become inaccessible.
I loved the game enough to buy all the expansions and play them through several times.
My wish for the game would be that units carried over somehow. It was great to see my units in PG progress from green to elite and encouraged me to be careful and avoid throwing units into meatgrinders. Although bashing at a city while suffereing bad losses in order to achieve your objective is often needed in UoC and is an interesting part of the game since it forces you to take risks.
I'm still looking for a game that would combine this kind of battle simulation with an economic simulation since as they say WWII was won in the factories.