Mechwarrior 5 is complete! It was fun stuff, I really enjoyed it. Like BattleTech, you run a small mercenary outfit that travels around the galaxy, shooting things for money. Between battles, you'll need to repair all damage to your big, stompy robots. You'll be able to buy/salvage new mechs and customize them with different weapon loadouts and armor. Unlike BattleTech, this one has live action, 3D battles instead of being turn based, overhead views.
The basic gameplay loop is pretty simple: fly to a star in a conflict zone, pick a mission you like, complete it, get paid, fix your mechs, and repeat until you get a lot of cash. When you do get a lot of cash, go mech shopping at some industrial planets. Repairing mechs is cheaper on those planets, too, so you'll also go there if you get thrashed. There's a campaign that provides a series of missions to run and a story to go with them. The story is full of weak sauce (THEY killed your dad, now you're going to kill them back - killing several other people along the way!?) and is delivered by talking heads, but the missions are fun.
I think the key to the game is the progression of mechs you use and fight against. There are a lot of strengths and weaknesses to balance as you grow your stable of mechs. Customizing them allows a lot of creativity, too. You'll have to balance whether you would like to bring another medium laser, or if it would be better to leave the laser at home and bring an extra ton of ammunition for your autocannon. Do you want to put that nice, high level PPC on your arm mount? Arms get shot off pretty often - maybe it would be better to put it in another mech's right torso? But torso weapons have to shoot more-or-less forward, while arms have a wider field of fire...
The game autosaves whenever you go to another star, whenever you start a battle, and whenever the battle finishes. You can also make manual saves, but NOT while a battle is going on. The battle has to be played out from start to finish! A typical battle lasts about 10 to 15 minutes. Some of the really big campaign battles have you trudge through a lot of scenery, so could take longer than that.
The DLC is worth it when on sale, IMHO. You don't need the DLC immediately and Steam offers the game+DLC in a bundle, so there's no problem playing the base game for about 10 hours and then deciding if you're going to play the game enough to justify buying the DLC.
The game also has a pretty strong mod scene going. There's some nice graphics enhancers and game play mods out there. A mod to help the game's AI (but allies and enemies) proved especially useful!