It's better now than it has ever been and it's perfectly doable on your own or at the very least with in game matchmaking (which is available in every mode thanks destiny!). With the underground you can rank up gear score super fast. When it hit I was like 140 gear score with just superior stuff and no high end. Playing since underground dropped I'm now like 231 and have all high end weapons and gear set gear. Underground offers the best rewards and that comes almost exclusively from the rank up reward so it's completely grindable solo if you choose or you can like I do, matchmake into harder difficulties and get more exp faster. I don't use mic and my matchmade groups always complete runs fairly smoothly since most everyone knows how to hide shoot or heal. Plus they've instituted a reward for season pass owners every 1st and 15th of the month a supply drop is dropped into the open city and you go and find it, fight off some level 32 enemies and get 3 high end or better items. I just got mine for today and got a 229 (max)assault rifle and a 268 (max too I think) holster. That was just freebies. I play it now in favor of destiny cause it's more fun the random dungeons and enemies in the underground are enjoyable and the overall game is more rewarding and I haven't even done a single incursion yet so I have those to look forward too as well.