No Galactus isn't the most powerful force in the universe but he is amongst some of the most powerful (a list created by users at Marvel.com)
One Above All
Heart of Universe
The Living Tribunal
Protege
Bubonicus the Plague-Bringer
Cosmic Egg
Sise-Neg
The Cosmic Compass - Death, Eternity, Oblivion and Infinity
Nemesis (V) (The Infinity Gems)
Infinity Gauntlet Holder
Infinity Well
Ultimate Nullfier
Galactus
Cosmic Cubes (Beyonder, Kubic, Shaper of the Worlds and Kosmos)
Roma/Omniverse characters
Time Variance Authority
Time guardians
GLORIAN
Abraxus
Tyrant
XORR THE GOD-JEWEL
Omega (IV)
ABYSS
Celestials
Desecretion Annex
Franklin Richards?
Aegis and Tenebrous
the Infinites
M'Krann Crystal
Phoenix Force
Goblin Force
Origin
Yahweh
Voyd
Seven Friendless
Master Order and Lord Chaos
Mistress Love and Sire Hate
Destiny (entity)
OBLIVION
The Watchers
Hawk God of Arcturus
The In-Betweener
The Stranger
Jakar
Five-Who-Are-All
the Makers
Khatylis
Eon (I)
Epoch
Era
Abrogate
Anomaly
COMPOSITE
Anthropomorpho
Hunger II
Infinity (II)
Un-Being
CORONER
Nebulos
Galaxy Master
Watchers
Vortex (II)
Unbeing
Rot
Those Who Sit Above in Shadow
Thor with Odin Power
Odin
Council of Godheads
Destroyer
Loki
Kurse
Malekith
Asgardians
Deities (All the gods not from Asgard)
Anthos
Elder Gods
Dark Gods
Mephistopheles
Satannish
Malevolence
Mephista
Death Gods (Hela and the like)
Hellstorm (Daimon)
Satana
Blackheart
Satana
MANGOG
ICE GIANTS
Chaos mites
Shuma-Gorath
KARVOC
Desak
Godstalker
Magus
Adam Warlock
Goddess
Drax
Thanos
Walker
Janie (The Female Warlock)
Kismet
SYPHONN
Ganymede
Silver Surfer (current Herald)
Morg
Galactus Heralds
Ardina
THE PUNISHERS
Fear lords (D'Spayre, Dweller-In-Darkness (I) )
Dream lords (Nightmare, Daydream, Dreamqueen)
Demons of the Realm of Madness (Dusk, Delusion, Dementia, Fetish, Megalomania, Necromancer, Neurotica, Obsession, Paranoia, Phobia, Psychosis, many other demons)
Belasco
Magik I/II
Nova (Richard Rider)
Annihilus
Blastaar
Praxagora
SPIRIT
CRUCIBLE
Zalkor
Ego
Kronos
Power Primordial
Elders of the Universe
Other (IV)
Captain Universe
Glorian
Captain Marv-Vell
Captain Marvel III/Photon
Mantis
Gladiator
STARHAWK
Beta Ray Bill
GAMORA
PHYLA-VELL
Asteroth
Count Abyss
Starbrand
Zom
Vishanti
Trinity of Ashes
Watoomb
Dormammu
Zarathos
Umar the Unrelenting
Dr Strange
Clea
Scarlet Witch
Atlez
ANTHRAX
ANTHROS
Balthakk
KRONOS
Anti-Being
BADOON (RACE)
MAXIMUM (BADOON)
Imperial Guard
DEATHBIRD
DEATHCRY
CERISE
ERIC THE RED
XTREAM
SHI’AR (RACE)
Super Skrull
POWER SKRULL
Skrulls
SUPREME INTELLIGENECE
INTELLIGENTSIA
RONAN THE ACCUSER
YON-ROGG
Stellarax
KREE (RACE)
Kree Sentries
BROOD
RIPJACK
MARTIAN (RACE)
MERCURIAN (RACE)
YONDU
NIKKI
TERRIAN
Phalanx
Enslavers
Eternals (Saturn)
Veeda Leebre
Sersi
WORLD MIND
Super Nova
Nova Corps
OMEGA CORE
BLOOD BROTHERS
Designate
Deathurge
BOUNTY
Pip
Hellphyr
Onslaught (entity)
Eternals (earth)
Black Bolt
Inhumans
Cyttorak (other members of Wager of Octessence)
Phaedra
CRIMSOM GUARDIAN
Quasar
BINARY
Pulsar
Starlight
Nebula
Jack of Hearts
MOONDRAGON
STELLARIS
Nebulon
Thunderstrike
Exiles base
SENTRY
STAR-LORD
STAR JAMMERS
Talon
TANA NILE
Deviants
IMPOSSIBLE MAN
Ancient One
Big Mother
S'ym
Chthon
Raggadorr
Translords (Deathwatch)
Archenemy
Akhenaten
Atleza
Diablo
Nega-Man
Mynx
High Evolutionary
DOCTOR DOOM
KANG THE CON’QUEROR
SCARLET CENTURION
Hyperstorm
Sphinx
Valeria
Man-Beast
LUNATIC
Pandemonia
N'astirh
Deacon Frost
Valtorr
Zxaxz
Modulus
Ikonn
Shathra
Nezaral
Olivier
Exemplars
Spite
Noble Kale
RIGELLIAN RECORDER
TERMINUS
Fin Fang Foom
Dragons
Squadron Supreme (all members for now)
Apocalypse
Adversary
Demon Bear (I)
Lilith
Exodus
Santa claus
RANCOR
Deadpool
MARTINEX
THANATOS
Mandarin’s rings
PSYCHO-MAN
Arkon
Thundra
BLACKOUT
DARKLORE
S.W.O.R.D.
SleepWalker
MAJOR VICTORY
GUARDIAN
Moon Knight
Machine Man
RED RAVEN
LIVING LIGHTINING
DIAMOND HEAD
MANWOLF
YELLOW JACKET (RITA)
SCRIER
Its exist in different versions but this is the last one i believe not sure they update the top constantly