Voila la liste d´après le magazine italian PSM de toute les armes et ennemis de ce Devil may cry 4 + un comparatif avec les différents opus 
ENEMIES
1) Scarecrows
2) Master Scarecrow (Seen both in video format and in some screens)
3) Frosts
4) Assaults
5) Blitz
6) Mephisto
7) White Knights
8) Gold Knight
9) Hell Dogs
10) Shark Demons
11) Ice Toad (Boss)
12) Berial (Boss confirmed re-appearance)
13) Echidna (Boss confirmed re-appearance)
14) One Winged Dark Knight (Boss)
15) Collossus (Boss)
16) Agnus Insect Form (Boss)
17) Vergil (very likely Final Boss)
18) Dante (First Boss with possible re-appearances)
19) Shadows (Confirmed to be in the game in some form)
(More enemies and bosses are still pending release)
Compared to DMC3´s Enemies
1) Hell Family (7 Total)
2) Hell Vanguard
3) Chess Family (6 Total)
4) Enigma
5) Arachne
6) Abyss
7) Blood Goyles
8) Fallen
9) Soul Eaters
10) Gigapede
11) Cerberus (Boss)
12) Agni and Rudra (Boss)
13) Beowulf (Boss)
14) Nevan (Boss)
15) Lady (Boss)
16) Arkham (Boss)
17) Doppelganger (Boss)
18) Geryon (Boss)
19) Vergil (re-appearing Boss)
20) Dullahans
Add in 12 for the variations of families of Hell family and Chess pieces.
Compared to DMC1
1) Marionettes
2) Sin Scissors/Sin Scythes
3) Death Scissors/Death Scythes
4) Beezlebubs
5) Sargassos
6) Plasmas
7) Blades
8) Shadows
9) Frosts
10) Nobodies
11) Fetish
12) Phantom (re-appearing Boss)
13) Nelo Angelo (re-appearing Boss)
14) Griffon (re-appearing Boss)
15) Nightmare (re-appearing Boss)
16) Mundus (Final Boss)
Technically speaking DMC4 already has more enemies than DMC1 and more bosses, so it certainly isn´t the least varieted enemy list in DMC. With DMC3, because of the families of very similar enemies it ends up that DMC3 has more enemies than DMC4 thus far but if you pack in the families as a singular type of enemy then you will see that DMC4 at least matches DMC3´s number. DMC2 actually has the most enemy count in a DMC game at well over 50 but the quality is extremely mediocre as you all know.
DMC4´s Weapons
1) Red Queen
2) Blue Rose
3) Yamato
4) Ebony and Ivory
5) Rebellion
6) Shotgun
7) Gilgamesh
8) Lucifer
9) Pandorra´s Box
10) Confirmed Spear-Like weapon for Dante
11) Semi-Confirmed Sparda Final weapon for Dante (read the Italian PSM translations clearly mentioning the Sparda sword for Dante)
That´s 4 Firearms, 7 Devil Arms already. The German site states 12 weapons but I think they were only counting Dante´s weapons or they didn´t include Yamato as a weapon.
DMC3 Weapons
1) Rebellion
2) Cerberus
3) Agni and Rudra
4) Nevan
5) Beowulf
6) Kalina Ann
7) Ebony and Ivory
8) Shotgun
9) Artemis
10) Spiral
11) Force Edge + Yamato Hybrid
12) Yamato
13) Summoned Swords
DMC1 Weapons
1) Force Edge
2) Alastor
3) Sparda
4) Ifrit
5) Ebony and Ivory
6) Grenade Gun
7) Shotgun
8) Nightmare Beta
9) Needlegun
(enfin j´ai fais que survoler donc, je verrais quid de cette arme dans le jeu 
)