For me, the difficulty changes too much depending on the number of characters. I usually play with 2-3 friends, and so far (4th Scenario of second adventure pack) we haven't lost once, even when getting greedy.
However, every single game (4 total) we played with 5-6 Players, we lost. 3 out of those 4 scenarios, we had closed all but one or two locations and the last player was one extra explore short of encountering the villain. Greed/inexperience of our guest appearences does play a part though. Saving a blessing for an explore when you could instead drastically increase the odds of making a closing check is an unnecessary risk, and if the henchman was close to the top of the location deck this will cost too much time.
I also played solo (1 character) with Ezren and Kyra up to the end of AP3. Kyra lost a few scenarios due wasting too much time healing up or failing multiple times on closing checks, but otherwise she has had no problems. Ezren had significantly less than 50% winrate. He does not really lose due to time but rather due to having less than 6(7) cards left in his deck and stopping exploring. Having neither heals nor Blessings does make it extremely difficult. I did start him out with 3 cures, but eventually he was fortunate enough to find new spells and thus unable to replace them. Now, any scenario with either shrine of Lamashtu or a villian with multiple combat checks, he only has a very small chance of succeeding.
I learned my lesson about unnecessary risks with Seoni.
Solo Seoni died when she had 5 cards left in her deck, and only one open location left. She decided to explore instead of surrendering when she had a blessing matching the top of the deck, a Wand of Force Missile, an attack spell, masterwork tools and some other cards irrelevant to the situation in her hand. I encountered the villain who summons a wrathful sinspawn. So I though ok, I'll just blast the summon with the wand, won't matter if I lose a few cards, and then kill the villain. I lost the wisdom check for the sinspawn (not much bad luck there, she didn't really expect to succeed). But then I rolled 3 ones and a two for the wand for a total of 5 out of 10 necessary. So she took 5 damage, had to discard her entire hand and then failed the recharge roll on the wand. She would have survived if I had either played the spell to kill the summon (auto-recharge), or if I had played the blessing (auto-recharge) on the wand or the wisdom check. Somehow I
failed to realize that a bad roll would kill her.