Wow that's a mean beastie for your first adventure! They are 8 or 9 hit dice monsters if I remember correctly.
I can't remember my first monster but I remember my first party. The DM got me to roll up 4 1st level characters, they were -
Groin The Groper - Male dwarven fighter
Legolam - male elven magic user
Eorache - female human cleric
Arrowroot - male human ranger
I've just looked and I still have the character sheets from when they were 4th level. I think the first creatures I met were kobolds or goblins.
One of my most memorable adventures was when my gnome fighter/illusionist was hit by a remorhaz, we use critical hit tables and triple damage was rolled. Now my gnome had a ring of fire shield (4th level magic user spell) and any hit that he took then the attacker took double. So I got whacked for 41 points of damage and was left on 5 hits but the remorhaz took double that and basically blew itself up around me! One of those really cool moments that D&D throws up and the story was told in all the taverns and inns and became part of the Legend of The Gnome.
Do you recall the first beastie you saw, the first time you played D&D? Mine was memorable, although not too romantic: an otyugh. (I'm actually pretty sure it was a neo-otyugh, but why split hairs..)