Yet those three big-name signings have been overshadowed by one which was not expected to be quite the hit he has become this season: .
A chance worth taking
The 24-year-old spent last term on loan at Eintracht Braunschweig and was therefore not a new recruit per se, although few anticipated that he would stick around for long heading into pre-season. However, he impressed Roger Schmidt so much during preparations for the new campaign that the new coach said: "Karim's not going anywhere - I want him."
The fact that it was Bellarabi who bagged Leverkusen's first goal of the season to down Borussia Dortmund at their own stadium was no coincidence either. Nor was it a fluke that it took just a record-breaking nine seconds for the net to ripple, while his equalising goal in the 1-1 draw with Eintracht Frankfurt on Matchday 17 was his eighth in 17 Hinrunde outings, all of which he had started.
Bellarabi, who also supplied four assists, was delivering on a promise he had made to himself. "I had set myself the target of really giving it a go this year," he said. "You don't get that many chances in life, which is why I wanted to make my mark right from the start of this season." He did just that, ensuring he took his second chance in a Leverkusen shirt. His first - from 2011 to 2013 - was incomparable, with a total of 18 appearances and just one goal to show for an injury-hit spell at the BayArena.
He seized his opportunity to play regular Bundesliga football with Braunschweig in 2013/14, laying the foundations for his dramatic rise back to the top in Leverkusen. Yet the technically-gifted and lightning-fast attacking midfielder has never been as strong as this season. "I reckon he's got four lungs, not just two," said his astounded team-mate Gonzalo Castro. "He's in scintillating form."
Bellarabi has shown that not just in flashes either, but on a regular basis. The Berlin-born star of Moroccan descent started the season so well that even Germany coach Joachim Löw could not resist the temptation to take a closer look, summoning him for his international debut in October in the EURO 2016 qualifier against Poland. Now it is hard to imagine a Germany side without him.
With a total of 26 appearances already in 2014/15, Bellarabi deserves his winter holiday (see below) perhaps more than anybody. "We're third in the table and that's pretty fine," he said after the most successful six months of his playing career. "Of course we could have got more than 28 points, but overall we can be really happy."