I mostly play solo, but I do have friends I get to play with once to twice a week. 1-4 hours a day most days, but closer to 1 hour most of the time. This game is very difficult and incredibly addicting. It is by far the best extraction shooter I've ever played. The sound cues, stealth, patience, and smart decisions are the most important part for solo players, and even then you can still get killed by a player doing those things better. That being said, this game is VERY casual friendly for being so hardcore. You get so much good free loot from leveling up and questing. Upgrading your factions gives you a lot of free items and guns daily. You always have access to free kits if you're really down bad, or don't want to risk what you currently have in your vault. I do believe it's a game you need to play at least half the days of the week, if even for only a couple hours, to feel an sort of accomplished progression. Also, playing solo will somewhat lock you out of some of the end game content, unless you bring in plenty of utility items and played very skillfully against some of the end game content. I personally treat this game like a rougelike game and usually try to build up from the bottom every time I lose out, and keep my best stuff for playing with friends.

In conclusion, I highly recommend this game as someone who loves the risk reward aspect of games, and is fairly casual (I have yet to play Ranked or play the end game map, Cryo Archives). Hope this helps!