My german cars have been all over the map. Ive had a couple of great BMW's 1998 540i, 2004 335i the wife had was great. Had some ok BMW - 2006 X5, 1996 318ic, and some absolute dog turd BMW's. The shitty ones are more recent, and have ensured that brand is dead to me. No more. Of my Porsche vehicles I can say they have all been fantastic. That consists of 2 911's (still have one, but it's recreational at this point), a 2012 Cayenne S that was absolutely awesome for the 100K miles we had it. The daily drivers we have now are relatively new and still under warranty, but so far so good on them. On the Panamera gts I have only done the 20k scheduled maintenance so far. Nothing else has popped up. The Cayenne we now have was acquired back in September so that one hasn't had anything going on yet other than burning an absolute ass ton of gasoline. Hoping they all work out as well as the 911 and former Cayenne. If so, we will continue to be satisfied customers.
I don't know that many people who drive Mercedes so I cannot say much about them. SIL has an S class, but it's brand new. It's beautiful. HAve several friends who have Audis, and they generally seem happy. I had an A4 for a short period of time, and enjoyed it. Nobody seems to be having any major issues.
I really love the styling on the current Alpha Romeo cars. I hope yours is one of the good ones. They all certainly pass the eyeball test. My BIL has an old mid 80's AR Spyder that he has had for probably 25 years. It's awesome. He did a minor restore on it several years ago. Great looking car, and fun to cruise around in on a nice spring or fall day.