Call of Duty: Black Ops debuts a new theme around the Cold War conflict whereas previous titles related to either World War II or modern age warfare. Developed by Treyarch, Black Ops seems to have a lot more in common with the older World at War than Modern Warfare 2 though.
Besides the fact that it's coming from the same development team, Black Ops essentially uses the older Call of Duty 4 game engine. To be precise the game runs on an enhanced World at War engine, which is in itself an improved version of what Call of Duty 4 used back in 2008. This new revision of the engine features a streaming texture technology also supported in Modern Warfare 2 that allows for larger levels, for example the "Payback" level where the player controls a helicopter. Additionally, lighting effects have been improved and the game supports 3D imaging rendered when using the correct hardware.
Before we get busy with the benchmarking to see how various hardware configurations handle this game, here is a quick summary of what's going on (courtesy of Wikipedia). As pointed out before, Black Ops takes place during the Cold War. The player mainly controls two characters: special forces operative Alex Mason and CIA agent Jason Hudson. The single-player campaign revolves around an experimental Soviet chemical weapon codenamed "Nova-6". The game includes locations such as the Ural Mountains in central Russia, Cuba, Laos, and Vietnam. Viktor Reznov, a key character from the Soviet campaign in World at War has been confirmed to return for Black Ops, joining Mason and the SOG in Vietnam. Dimitri Petrenko, the Russian protagonist from World at War also makes an appearance.
The online multiplayer mode of Black Ops retains the experience points and unlockable reward system that has been kept since Call of Duty 4. "Create-a-Class 2.0" allows enhanced personalization with appearance items as well as upgradable perks: weapons are extensively customizable with clan tag writing, emblems, attachments and camouflage painting.
For the first time in the series, clips from online gameplay can be recorded. Some PC specific features that were taken away from Infinity Ward's Modern Warfare 2 return, such as lean, mod tools, the developer console and dedicated servers. Dedicated servers are exclusively provided by Game Servers. Steam is the exclusive platform for Black Ops on the PC, so the game is protected by Valve Anti-Cheat.