Lines 2 and 3 of Athens are pretty good when the system doesn't shit its own pants, which it does at least once a week. It's worth mentioning that most stations have no Internet access and that the electronic signs in the stations have no clue when the next train will arrive (it's somehow worse than bus electronic signs, despite the fact that buses are affected by traffic and the metro isn't). The airport part of line 3 is served every 36 minutes, usually with a delay (that messes up the rest of the line too).

Line 1 is very old. Second oldest "metro" in Europe, functioning since 1869, newer than only London (Istanbul is third I believe). People call it the "Electric", a nickname that stems from its electrification in 1904. It's quite bad though, with infrequent trains that need maintenance and sketchy parts of its path. But it's also pretty, because most of it is open-air.

There is also a line 4 in the way, which is supposed to help many areas that are still out of the network when it opens. It's expected in 2032, instead of 2029 that was the previous official year of opening. There are also several expansions in different stages of consideration for lines 1, 2 and 4 (but not 3, as it is considered complete, going from the airport to the port of Piraeus).

The tram is one of the most beautiful transportation systems I've seen (particularly the coastal line), but it's also slow, infrequent and unreliable, with trams running every 20 minutes at times.

The suburban railway is awful, running every 30 minutes and often having skipped routes and 20+ minute delays, as well as bad signage. It also has lots of level crossings on the Piraeus branch, which slow it down a lot.