I'm currently including German Volume Training or GVT into my training programme. This consists of 10 sets of 10 exercises, but can also consist of fewer reps per set, today for example I did 6 reps per set, which I found more manageable. This type of training is purported to add muscle in a shorter timespan than the more usual 3-4 set training protocols. It's a bit early to tell whether it's helping me add muscle more quickly, but the main benefit that I find about this type of training is that it's easy; in each session you choose a body split, i.e. chest and back, legs and abs etc, focusing on compound movements which bring in multiple muscle groups and typically will focus on 2 exercises supersetted with 90 seconds rest in between. I then finish a session with 2 related exercises (3 sets) and a quick HIIT. That's it I'm done. I'm definitely 'feeling' my muscles a bit more the day after.
Psychologically, ten sets seems like a lot, but you just chip away and make sure you have something to read in the 90 seconds rest. I haven't been doing this every time I'm in the gym; maybe once or twice per week. Let's see whether it's worth adding this method more permanently!