how da fuk did Atalanta of all teams get into the CL anyway?
A combination of ineptitude from the larger Italian clubs with money (Milan, Roma etc) and the work of Gasperini who manages to build teams that are greater than the sum of their individual parts.
They would have qualified for CL 2 years ago when they finished 4th but Italy only had 3 spots back then. That was the team of Caldara, Conti, Cristante, Gagliardini, Kessie, Petagna and Krle's cousin Pesic. A lot of those guys were sold for good money to bigger clubs and none of them have really worked out. Some because of injury, others because of a genuine lack of quality as they were made to look a lot better than they actually are due to Gasperini's system.
The funds from those player sales were used to build the next Atalanta team with Ilicic being the most notable addition. Last season they arguably played the best football in Italy and deservedly finished 3rd despite having the 14th biggest wage bill in the league. A great achievement from what is essentially a provincial club.
They play very attacking and managed to score the most goals in the league. However, they are suspect defensively due to how open they play and are prone to losing to smaller sides because of this.
This season they are clearly not playing at the same level and were fortunate to beat a limited Genoa side on the weekend. Their squad is very thin and not really built to compete on multiple fronts. Even with CL money they didn't really add much in the summer and lost their best defender, Mancini, to Roma. They are a couple of injuries to key players from a slide down to mid-table.
Last season they were eliminated by Copenhagen in EL qualifying. Whilst the margin of their defeat today was a surprise, the result was not given Dinamo is certainly a stronger opponent than Copenhagen. Italian teams often have difficulties dealing with the intensity of teams on the continent.