Your friend is in the minority then. I think that's literally the only person who I've heard of who watched it and didn't like it.
And he started cooking meth cos he saw one of his old students cooked it, poorly, and wanted to team up. It's a fucking great show man, you should try it before you knock it!
They are indeed -they hold a pHd in medicinal chemistry, so they found the scenes involving methamphetamine synthesis painful to watch. That's what really spoilt it for them. However well acted, however well the story arc was constructed, the truth is that at the scales involved their is only 1 route that just 2 people could possibly have adopted to reach the scales involved. Catalytic hydrogenation.
The PROBLEM with catalytic hydrogenation is that it doesn't make good TV. You simply place the precursors into a very large Parr hydrogenation unit (or indeed multiple hydrogenation units), pressurize with hydrogen and watch the pressure slowly drop until calculation show that the reaction is complete. It will work equally well if one uses pseudoephedrine or PMK as the main precursor.
No explosion hazards, no 'exciting' chemicals, noxious gasses or indeed anything 'visual'. Very dull to watch,
BUT it's not a route any TV series could possibly disclose because it's carefully not mentioned by the DEA. And before you ask, we both knew of a very large meth lab in the US that was using catalytic hydrogenation to produce both meth and MDMA. The DEA did eventually find it, arrest the guy who was running it (spitball from The Hive) and AFAIK he's still in prison.
I do realize that it's a very nerdy reason but when you actually know how it's actually done when minimizing the number of workers is a key driver, it kind of spoils it. While I accept that the vast majority of meth labs don't use catalytic hydrogenation, they are either rather small scale or they require dozens of workers.
The ECMDDA has some nice images of large-scale European amphetamine labs and they would need about 8 people per shift (you run those things 24 hours a day) and likewise the DEA has some images of the Mexican 'super-labs which would need dozens of people per shift. In both cases, I'm 100% certain that the REAL chemist wouldn't go within a mile of those labs.
But just 2 people? No.