The Ashes series games aren't just impressive mods, they are some of the best FPS games of all time. They combine the best parts of mid-late 90's game design with the best aspects of modern game design. The visuals and audio are beatifully designed and highly functional whole, the soundtrack is great. The gameplay is wonderfully paced and balanced while the level design is amazing. Ashes games stand tall on their own merits and the fact they are built on DoomII/GZDoom tech is merely an interesting fact, not an excuse for anything as these games need no excuses.
Combat Missions are great tactical wargames that were way ahead of their time when they came out and have also aged really well. They are more like proper combat simulators than typical RTS Company of Heroes, Men of War) or turn-based strategy games (Panzer General, Panzer Corps): Real military tactics work great and are required due to the highly authentic gameplay. The turn based we-go system makes battles of any size easy to manage, although it typically takes several minutes of real time to plan one minute of game time. The bigger the scenario, the more time it takes. Some patience is definitely required. The controls will take a while to learn and remembering some hotkeys will help a lot, but after that's done you are left with a very functional control system that makes a very deep game relatively easy to manage. Due to the highly realistic nature of the game, the gameplay itself is very easy and intuitive to learn if you are at all familiar with real WW2 tactics. Reading the manual is highly recommended. Barbarossa to Berlin is massive game that covers the war on the entire Eastern Front from 1941 to 1945. Despite the huge scope the great attention to details is obvious. The historical weapons, units and armour are well researched and modeled. The graphics of the game weren't the greatest even when the game came out but they are clear and haven't aged too badly. They definitely serve their purpose. Even today very few games (mainly the newer Combat Mission titles and Graviteam games) can compare to the old Combat Missions and in some areas the old games still surpass them. All the combat mission titles are worth playing to anyone interested in realistic tactical games and Barbarossa to Berlin is probably the best of the three.
Blood Money combined and refined the best parts of previous Hitman games. The gameplay is classic Hitman at its purest from before the series started getting more shooter like. The missions are great with no ill-fitting filler content like the jungles of Codename 47 or the Japanese snow level of Silent Assassin. Solutions to missions feel more open than the heavily scripted machinations of the rebooted Hitman games. If you are going to play one Hitman game, I recommend this one.
In terms of gameplay World in Conflict falls somewhere between Company of Heroes and Wargame titles. It's not quite as low level tactical as CoH, but the scale also never gets huge and you have to micromanage your units quite a bit. There's no base building which is a big plus in my opinion. The biggest specialty of World in Conflict are the airstrikes and off-map artillery assets that let you unleash some of the most satisfying destruction in any RTS game on the battlefield. The graphics are of course somewhat dated by now but they have aged very well and the visual style is still great. Both campaigns are good and have a lot of high quality dialogue and cut-scenes to flesh the game out even more. The game is definitely worth playing to anyone who likes RTS games (I haven't played the multiplayer so this review is only about the single player campaigns).
Jedi Outcast has nice plot, good missions and is a very good game overall but the most important feature of this game is its lightsaber combat. The next game in the series, Jedi Academy, might have had more lightsaber types and more lightsaber duels but in Jedi Outcast the fights and fighting mechanics were much better (also the plot and missions in Outcast are better). For starters lightsabers are deadly, most fights end in a single good hit. The lightsaber duels are usually intense struggles of dodging and parrying until one side makes a mistake. For comparison, in Jedi Academy the fights are usually much shorter, easier and you usually need several good hits to kill an enemy (a ridiculous amount of hits in case of some bosses). This simplification was probably a direct result of the added lightsaber types. Jedi outcast also did a lot better job in making the lightsaber duels feel special, instead of wiping out lightsaber users in every second room like in Academy, there were only a handfull of force users in the game and every one of those encounters felt memorable and challenging. Jedi Outcast is the best star wars lightsaber/jedi game there is.
