My first match saw me fight a entire Genestealer Cult Army.
Yeah, Cult Ambush deployment is bullshit, though can go poorly for the Cult.
Looks like he got some godly rolls if he pulled it off like that. Note it was worse on you due to DWs limited model count. Teleporting large blobs of cheap gribblies are pretty much nullifies any chance of getting a good position on him.
There's only a handful of ways to prepare for this (like taking Servo Skulls or Inquisitor Greyfax, as it mostly runs by Infiltrate rules) but you need to know it's coming beforehand for that
Deathwatch itself doesn't really have any really good counters handy, though Templates should clear a lot of it up. Anyway, at that point the only thing you can do is shoot every weapon you can (and charge any Neophytes you safely can).
My second game was seriously just an absolute slaughter even worse than what happened in my first game. I was fighting a tau running a farsight enclave setup.
A poor matchup, as their shooting will thin your already thin numbers... And as you found out, if you're visible, you can be shot. Only real way to fight Tau is good use of LOS blockers (assuming those are even ON the terrain) and blowing them up in small parts, and/or pulling off a good multi-pronged assault.
Enemy FW walker dude was presumably this one
. Assault 2 S6 AP2 flamer with 6" torrent, that model was a quarter of his points and he had another one, apparently. Dunno what type it was, but even the 'normal' XV104 Riptide is somewhat under-costed, and having two of the big guys in a 1000 points is pretty cheesy. Nothing you can do about the enemy list though. Best tip I have it to always ask if you don't know what a specific enemy can do, especially big and mean-looking ones.
My final game though it should be noted was due less to bull shit stuff and more just a combination of god like and horrible rolls.
Actually, there's some bullshit there. He's not actually allowed to Gate of Infinity across the board and Assault in the same turn, as Gate of Infinity uses Deep Strike rules. Grey Knights also have Personal Teleporters for rapid relocation, but those too will not allow for an assault the same turn. Shooting alone could have done a good amount of damage still, but as I'm guessing that was your Grav-cannon Devastator squad being removed from play, that's a big one for this game.
So all in all the day was a complete slaughter for the old deathwatch and make me reconsider my life choices, i've got two land raiders and another librarian coming sometime soon so hopefully for the next one i can hold my own because Emperor mein god that was some bullshit XD. I truly wish i had a better report to give you after the help you gave me in realizing rules and abilities i never even knew i had (I did a fair amount more research after the last post and realized alot of rules i wasn't using effectively) But alas it was not to be. I think my final points count was like 3 maybe 4, possibly 2, you know imma just go with shit
FWIW, small elite forces are actually among the hardest armies to learn to play, especially at high level. An IG player can lose a Guardsmen squad and just shrug as he's got another 50 where those came from... the fewer models you have, the more you need to get the most out of each. Make sure you check the rules as you play friendly games, both for your own army and the enemy's as knowledge very much IS power. You'll find you'll do better the more you play, so... play more