One thing I do not like about the name "metroidvania" is that it focuses on two specific console games (from 1986 and 1997) while, around here, consoles were not popular, games were played on 8-bit computers (Amstrad CPC which I had, ZX spectrum, Commodore 64, etc.), and there were many cool games on these computers that were at least proto-metroidvania, and seem almost completely forgotten by now (even if Metroid was probably better than them).

I mean games with the following properties:

• 2D platformer gameplay (that excludes 3D isometric platformers like Head over Heels or Sweevo's World, and top-down games -- I do not recall any good top-down games but Zelda is an obvious console example)
• you collect things that are at least a bit more interesting than "collect everything" (that excludes, for example, Jet Set Willy)
• the world is not subdivided into levels or clearly linear
• in a modern metroidvania you get new movement/combat abilities during the game, and areas are gated by this abilities -- this is "proto-metroidvania" so this very specific feature is not necessary

I remember the following:

• Pyjamarama (1984) -- the world was quite small (34 screens) and consequenly not really exploration-focused, but there were lots of items that you had to find specific uses for (like scissors to cut balloon, etc.), the game also had sequels in similar style (Everyone's a Wally, Three Weeks in Paradise).
• Impossible Mission (1984) -- do not remember much, but I think it barely qualifies
• Chuckie Egg II (1985) -- a rather big world (120 screens), you had to collect ingredients for a surprise egg, interesting items included baskets (carry more ingredients), ladder, power switch. One interesting thing is that included a true save feature (many sources claim Legend of Zelda as the first game having that, but that is because they focus on consoles, it was a rather obvious things on computers -- the first game I know with true save feature is Rogue of "roguelike" fame, 1980/1981)
• Starquake (1985) -- about 500 screens, powerups like ammo/temporary platforms/health/lives and items like keys and access cards
• Hero of the Golden Talisman (1985) -- seeing this called metroidvania in Wikipedia has inspired me to collect these games. Items like special weapons to defeat bosses (did not look different from standard otherwise), keys, and candles. IIRC the map was rather linear (it was labyrinth-like but you did stuff in a specific order)
• A View to a Kill (1985) -- I do not remember much about this one
• Finders Keepers (1986) -- you could collect items that acted as keys or could be combined or sold (also had sequels such as Spellbound)
• Cauldron II (1986) -- I would qualify this as metroidvania, items could be used to cancel monsters and open doors, among others. Interesting platforming where you play as a jumping pumpkin. (Cauldron I/II switched protagonist/antagonist, IIRC Cauldron I was less metroidvania-ish.)
• Sacred Armor of Antiriad (1986) -- this was too complex for me, but I remember my older brother playing it... you start as a man in a loincloth and then you find a high-tech suit and powers for it like flying and shooting.
• Saboteur II (1987) -- items maybe not very interesting, but I think it is a better early example of female protagonist than Metroid. A few hundred screens, I think. (A sequel of smaller Saboteur.)

Any more I am missing?