It was a revolutionary design, the first all metal monoplane fighter and the first fighter designed as an energy fighter. At the start of the war, it was the fastest fighter plane.
Great plane for the aces but a punishing machine for the rookies to fly. The lack of checklists and other similar SOP's in the Luftwaffe also led to many casualties among the rookie pilots in the late war. It's Achilles heel was it's difficult ground handling.
Summed up nicely by General Adolf Galland:
"Every fighter pilot expects his plane to perform, the Me-109 expects it's pilot to perform"
The early 109s had two 7.9mms on the cowling which fired through the propeller arc and two 7.9mms in the wings.
The E variants had two 7.9mms on the cowling and two 20mms in the wings. The E-4 and E-7 20mm cannons were better than the earlier 20mm cannons as they fired the improved high explosive incendiary rounds.
The F variants didn't have the wing mounted cannons, instead they had a single 15mm or 20mm(for F-4) firing through the propellor hub. If needed, they would carry extra two 20mm cannons on external gunpods which were mounted on the wings, though they reduced the performance of the plane but were suitable against bombers. The G variants had the same armament.
The later variants replaced the two 7.9mm mgs with 13mm mgs.
In short, most of the 109 armament was in it's nose hence there was never an issue of gun convergence and sight adjustment.
In other fighters like the spitfire with wing mounted guns, the convergence and sight was set on the ground and wasn't a big issue.(they had tracers to adjust their aim after all).
There were plans to replace it however performance wise, it was not obsolete by any standards thanks to the upgrades. The K variant could easily hold it's own against the allied fighters of the late 44 and 45, but the fuel shortages coupled with the lack of experienced pilots meant that it could not be utilized to it's full potential. This plane was fast and maneuverable by late war standards despite it's poor ground handling, and steep learning curve.
109 was a high altitude fighter unlike the Fw-190 which did not excel at high altitudes(except the 190-D) because of it's radial engine, and in many cases the heavily armed Fw 190s were employed against bombers with me 109s as their escorts. The bf109 K, its latest model was performance wise one of the best planes of the war.
