I guess this is really late, and I've been out of the playtest forum for a while so that my opinions wouldn't be colored by the flurries of posts.
Also, this is a work in progress, as my group and I have little time between college classes, work, etc. Our group tends to play lower level games, so that has been the focus of our scrutiny, and we'll be working on higher levels as time permits.
1st Cantrips, spell combat
2nd Combat casting
3rd Magus arcana
4th Arcane weapon
5th Bonus feat
6th Magus arcana
Spell Combat (Ex): A magus has learned to cast spells and wield his weapons effectively at the same time. This functions much like two-weapon fighting, but the offhand weapon is a spell that is being cast. To use this ability, the magus must have one hand free, while wielding a light or one-handed melee weapon in the other hand. As a full-round action, he can make all of his attacks with his melee weapon at a –4 penalty. He can also cast any spell with a casting time of 1 standard action from the magus spell list. He must cast this spell defensively, and he takes a –2 penalty on the concentration check. If the check fails, the spell is wasted, but the attacks still suffer the –4 penalty. A magus can choose to cast the spell first or make the weapon attacks first, but he cannot cast the spell between weapon attacks if he has more than one attack. Casting a spell in this manner does not provoke an attack of opportunity. The magus must have one hand free to use this ability, even if the spell being cast does not contain somatic components.
Combat Casting (Ex): A magus receives combat casting as a bonus feat at 2nd level.
Magus Arcana: As he gains levels, a magus learns arcane secrets tailored to his specific way of blending martial puissance and magical skill. Starting at 3rd level, a magus gains one magus arcana. He gains an additional magus arcana for every 3 levels of magus attained after 3rd level. A magus cannot select a magus arcana more than once. Magus arcana that affect spells can only be used to modify spells from the magus’s spell list unless otherwise noted.
Spellstrike (Su): Whenever a magus casts a spell with a range of touch from the magus spell list, he can deliver the spell through any weapon he is wielding as part of a melee attack. If successful, this attack deals its normal damage as well as the effects of the spell. This ability does not grant the magus a free melee attack—such attacks must be made normally. Alternatively, a magus can make a free touch attack with his free hand instead of delivering the spell through his weapon, as normal.
This is a very small and workable change that we feel better expresses the Magus's core ability from the outstart of playing. Level 1 is still strained, but it is not unplayable, even though the penalties are heavy. Giving combat casting as a bonus feat makes the 2nd level shine as the spells start showing up more frequently in melee combat. At 2nd level, my player expressed that he was glad to be able to actually describe his actions in the way he imagined them being played out with the class.
We moved Spellstrike into the arcana options. Originally, we had put it in the level 2 slot, but when we replaced it with combat casting, we decided it was better as an optional element. We are working on coming up with arcana ideas of similar utility. None of us like sacrificing spells for temporary bonuses to hot or to AC, so those arcana were ignored.
It was proposed that making Spell Storing an option for Arcane Weapon might negate the need for Spellstrike. However, we also feel like the Magus is already a bit bland because of this feature. Arcane weapon is nice for the cost, mechanically, but it lacks flavor, because any character can buy the effects that this class feature produces.
Overall, after some tweaking, and without trying to change the nature of the class, we feel like this is a very solid starting point, but it does need some more enticing options. Also, looking forward, I think many people would rather forgo heavy armor for other abilities. We didn't give that much thought, but after some debate, we decided it isn't as desirable a feature.
Summary: Spell combat is awesome but is underplayed. This is the main concern, despite my personal focus on making spellstrike work. We would like to see more options for spell combat, possibly along the lines of delayed attacks (magically readied, like a ward/rune in an adjacent square) or placing a rune that allows the magus to cast spells from a square he isn't occupying. I don't know how these would work, I just told the guys I'd put the suggestions up.
Thanks for letting us participate, Paizo.