I've taken back up the mantle of GM, and as we are 2 months into our campaign, mostly getting into the groove of this again.
One problem I'm noticing, or rather my players are noticing is lack of detail. I try to describe as much as possible, but I don't always give all the details needed sometimes. Two examples from today's session.
The party scout goes through the barrier, attempts to punch the one bandit that is clearly concentration on the protective barrier, gets blasted by magic from everyone inside the circle (making sure to count the effects to the party) and fails a will save, teleporting him back to the rest of the party. Scout goes through again, gets blasted again, but manages to hit the bandit and the bandit fails his concentration check, barrier goes down. Party rushes into to fight the "front line". Bandits have spread out in a circle due to the scout having gone around the entire perimeter at least twice before breaking in, so there is no real front line. One of the party gets mad as he now realizes none of the bandits have weapons, they are all mages, and he could have waltzed right to the back and take out the ones concentrating on spell in the middle of the circle.
During combat, there are four people always concentration on a spell, which the party didn't roll high enough to tell exactly what was going on, but could tell it was some kind of creation/polymorph/summoning spell using the wrecked caravans as material. The bandits are throwing bodies to keep this spell going. If one of the ones concentration on the spell dies, another jumps in, sometimes promoting AoO from movement, to have 4 people on the concentration at all times. The cultists/bandits never say a word in front of the party and their clear defined leader is silent as well. Orders were given while the party was hiding in ambush and the cultists knew what had to be done. Summoned golem nearly wrecked the 8 person party (4 NPCs they found, and asked for help from). The party said afterwards that it seemed fishy the spell didn't seem to have significance/the end result was still indelibly powerful and happened "right as they showed up".
I don't want to tell them that their two minutes of waiting and the cultists clearly throwing bodies on the spell without the party doing anything about it, was what made the monster so powerful, but it could have been worse. I was tracking full rounds of concentration for how powerful the monster would get, and this was more of the middle ground for what could have happened.
I know some of this isn't describing as much as possible, but I'm not sure how much the party should be asking or looking for clues. This session seemed somewhat sour for most of the players, and I'd just like to get some advice on trying to steer them in the right direction of things without giving long out of character explanations of things that are going on the the background.