I used to be a big fan of Gintama. However, after analysing the series more and with the current state of the series, I can't really say that now.
To start off, the plot, when it remembers to return after several gag arcs, is pretty much a poor man's Rurouni Kenshin with sci-fi elements. It had the potential to be good, but is ruined by inconsistency in tone due to not just the constant swap between serious and comedic arcs, but primarily the existence or non-existence of the 4th wall because of it. It's almost impossible to have a serious plot with clear limits if a character has reality bending powers of gag manga in a previous arc. This causes Gintama's current transition into primarily serious story arcs to not hold up in retrospect due to how consistently inconsistent it is. It also doesn't help that with the current story had countless last moment saves and talk of willpower in generic Shonen fashion, as well as the build up for many characters ending up being poor (eg. Kamui being poorly handled in terms of motivation during his fight with Umibozu).
Speaking of the gags, whilst I like a good reference now and then, I must concede that obvious referential humour is one of the lowest forms of humour from a critical perspective. This wasn't so bad in the earlier arcs, where the references to anime/manga tended to be play on words and there was an equal reliance on slapstick and running gags for it's humour. However, after the first 100 or so episodes, these references became gradually more prominent and more self indulgent. There's a clear difference between a pun and outright copying another series whilst a character says something like "This is just Dragon Ball, isn't it?". Gintama's tendency to overly reference Shonen Jump series makes it feel derivative and more like an advertisement for these works, making most of the series referenced better by default.
Getting onto the characters, whilst each of them had an interesting backstory and personality at the start, the difference in tone and the build up of serious arcs only for the switch in tone caused what could be good opportunities for character development to be ruined. For instance, the arc involving Okita's sister made it seem that Okita would change his attitude towards Hijikata, or at least stop doing the bazooka gag, but things go back to normal by the next arc. Same with Tsukuyo being stuck as a typical tsundere, despite the many opportunities for her relationship towards Gin to change. It also doesn't help that due to it's length, running character gags have become extremely repetitive and unfunny for the most part. You can't exactly say gags like Kondo being called a stalker/gorilla or Shinpachi being worthless beyond his glasses have much impact after they're used several dozen times.
I liked the first series of Gintama since even though many of the flaws I listed were abundant, it could be seen as providing all the positive elements of the series, though I'd still say it's far from the best comedy anime. The other seasons before the Shogun Assassination Arc were basically just more of the same, however, with scarce build up for a vapid payoff. Dropped the manga around chapter 543 or so and the anime halfway through the 2017 series.
Gintama (2006) - 6.5/10
Gintama (2011) - 5/10
Gintama: Enchousen - 4/10
Gintama (2015) - 6/10
Gintama (2017) - 3/10
Overall Anime score/Manga score - 5/10
