How many eps did GR write that had aliens in them anyway.
I am not sure if you actually meant episodes that GR wrote himself, or simply episodes filmed, as IMO if it were on screen it is genuine Star Trek. Because if you think aliens were a rare occurrence on TOS, then I wonder if you actually watched the all the episodes.
By my admittedly quick (and perhaps containing a few errors) work, here is a list of TOS episodes featuring aliens, both humanoid and non-humanoid. As
The Wormhole has stated, the Preservers may be responsible for the exitence of some of these aliens.
The Man Trap (Non-humanoid)
Charlie X (Non-humanoids come to get Charlie))
What Are Little Girls Made Of? (I am assuming Ruk was made in his creators' likeness)
Miri (VERY humanoid!)
The Corbomite Maneuver (humanoid)
The Menagerie (humanoid)
Balance of Terror (humanoid)
The Galileo Seven (humanoid)
The Squire of Gothos (Non-humanoid)
Arena (Non-humanoid)
The Return of the Archons (VERY humanoid!)
A Taste of Armageddon (VERY humanoid!)
The Devil in the Dark (Non-humanoid)
Errand of Mercy (Non-humanoid)
The Alternative Factor (VERY humanoid!)
Amok Time (humanoid)
Doctor Who Mourns for Adonis? (humanoid?)
The Apple (VERY humanoid!)
Catspaw (Non-humanoid)
I, Mudd (I am assuming Norman was created in his creator's image)
Metamorphosis (Non-humanoid)
Journey to Babel (humanoid)
Friday's Child (VERY humanoid!)
The Trouble with Tribbles (humanoid)
The Gamesters of Triskelion (humanoid)
A Piece of the Action (VERY humanoid!)
A Private Little War (VERY humanoid!)
Return to Tomorrow (Non-humanoid)
Patterns of Force (VERY humanoid!)
By Any Other Name (Non-humanoid)
The Omega Glory (VERY humanoid!)
Bread and Circuses (VERY humanoid!)
Assignment: Earth (Isis is?.....)
Spock's Brain (VERY humanoid!)
The Enterprise Incident (humanoid)
And the Children Shall Lead (Non-humanoid)
Is there in Truth No Beauty (Non-humanoid)
Spectre of the Gun (Non-humanoid)
Day of the Dove (humanoid)
For the World is Hollow and I Have Touched the Sky (very humanoid!)
The Tholian Web (Non-humanoid)
Plato's Stepchildren (humanoid)
Wink of an Eye (VERY humanoid!)
The Empath (humanoid)
Elaan of Troyus (humanoid)
Whom Gods Destroy (humanoid)
Let That Be Your Last Battlefield
The Mark of Gideon (VERY humanoid!)
That Which Survives (humanoid)
The Lights of Zetar (Non-humanoid)
The Way to Eden (humanoid)
The Cloud Miners The Savage Curtain
All Our Yesterdays (VERY humanoid!)
Trek has always been about "seeking out new life and new civilizations", so I would feel shortchanged by a Trek without aliens. I don't mind a few forehead bumped aliens here and there, as I have already suspended my disbelief a great deal by sitting and enjoying the show. With special effects and prosthetic applications as good as they are nowadays, we don't have to smirk at the likes of original pig-faced Tellurites. I would really like to see more non-humanoid aliens now, though, since the effects today are so much better.
Although I really like 2001 and nuBattlestar Galactica, Trek is not these nor (thankfully) Space 1999 or Buck Rogers.