Dwarfs!? is a strangely addicting game. If you enjoy arcade games, where the main objective is to beat your high score (or someone else's high score), you'll probably love this game.
The way you score is by getting as much gold as you can, while trying to stay alive--but, you're dwarfs aren't the brightest and will insist on digging into caves filled with water, lava, and monsters, so you'll have to keep a close eye on them, which becomes harder and harder as the game progresses.
The F2P version has the two easier difficulties unlocked and each can be played in 5, 15, 30, and 60 min sessions (but beware, you cannot save the game mid-session).
The only problem I've encountered is in long games, where you have thousands of dwarfs in the field at one time, my computer starts to lag--which makes the game very difficult and frustrating to play.
Overall, this is a fun, simple, casual game that can keep you entertained for hours or opened for a quick 5-minute session.
[NOTE: If you buy the full version, your personal scores and achievements will transfer, but the F2P version has different global leaderboards, and your global score will not transfer.]
[EDIT: For those wondering, I personally own the full version (non-F2P), which is why my play-time on the F2P version is so low.]
Concerning the DLC...
Dwarfs - F2P Skirmish Pack (Recommended): Comes with 3 modes (Sandbox, Rush, and Dark). Rush and Dark modes bring new challenges to the game and can be a lot of fun. In Sandbox, you can experiment. In Rush, dwarfs spawn CONSTANTLY and you can only let 200 die. In Dark, you cannot see where caves or minerals are located.
Dwarfs - F2P Difficulty Pack (Recommended): Unlocks the two harder difficulty levels (Hardcore & Tedi Hardcore) for Arcade mode.
Dwarfs - F2P Endless Mode Pack (Not Recommended): Exactly like Arcade mode, except it's endless and you're allowed to pick the map size as well as the difficulty. Beware lag. Also, no high score is recorded.
Dwarfs - F2P Summer Carnival Pack (Extremely NOT Recommended): Was a prize for a Steam summer sale years ago; a very simple mini-game that is completely different than the base game.
Dwarfs - F2P Base Defend Pack (Not Recommended): A cute little tower defense mode that's rather different from the base game.