In SR3, cyberware is easier to take, because you can take a geas for the Magic loss (assuming your GM has the Awakenings book), or have a power focus, which raises your effective Magic for determining whether a spell does physical Drain or not. Also, you could use the fetish or exclusive limitations for your high-Force spells, lowering their effective Force for Drain purposes. Keep in mind that these methods all have drawbacks (minor ones, but still something to keep in mind). On the flip side, it doesn't seem to be quite as useful - it's nice to have, but it's easier to do without it if you prefer.
Some spells are good choices in either edition - mana/stun/power bolt/ball, heal, improved invisibility and/or physical mask, levitate, some others. Mental manipulation spells are still good, but in SR3, they require a threshold of successes to work, so they aren't quite as easy. There are no indirect combat spells - they are classified as manipulation spells, instead.
Increase Reflexes is not success-determined, but taken at levels (+1 to +3), and even the +3 level is not that powerful - unlike wired reflexes, it only increases dice, not Reaction. So while the Increase Reflexes +3 spell and Rating: 1 sustaining focus combo may seem cheesy, it really isn't. It lets you go more than once a round, but it is really only the equivalent of wired reflexes: 2. Most street samurai will have much better initiative than that - at least you'll go before the grunts do.
Some other changes from SR4 -
Magic is not part of your dice pool, and there is no overcasting. Spells are bought at a set Force, and must be repurchased if you want them at a higher Force. So get them at the highest Force you will want them in the first place. Generally, any combat or resisted spell should be at 6, useful spells such as levitate can be 5, and others you can get away with lower than that. The Force of the spell is also the target number to resist it. This means that a Force: 6 spell is twice as hard to resist as a Force: 5 spell! Magical foci are easier to get at higher Forces, although for a full mage, this generally means taking Resources: B.
Drain is different between conjuring and spellcasting (for conjuring, you compare your Charisma to the Force of the spirit to determine what the Drain is - elves make good conjurers, because not only are they rolling more dice, but chances are, they are resisting less Drain, too). Note that trolls, while good at sorcery (they have a slightly smaller spell pool, but can cast and soak Drain just fine), are not very good at conjuring due to their Charisma penalty.
Shamans and hermetic mages are very different. Shamans summon on the fly, and don't have binding. Hermetic mages can bind elementals and place a number of them on standby, but they can't summon on the fly (except for watchers). Hermetic mages also tend to be a lot more expensive - they need expensive libraries and conjuring materials, while shamans only need a cheap shamanic lodge. Generally, spirits have a wider range of useful powers, while elementals offer more brute force and raw power (adding dice to your spells, etc.).
Trolls make decent combat sorcerers, but have more disadvantages as full mages, where their lower mental Attributes make them less effective when astrally projecting or summoning spirits. Still, a troll in a top hat would be pretty cool.
Houngans are fun to play, but keep in mind that possession is not that effective until you can get invoking (to summon them in their great form - normal possession does not give you invulnerability to normal weapons as it does in SR4) and channelling (to have a small measure of control over the spirit). Unlike SR4, loa can do more than possess a host - they can also perform the same services that a watcher can, or can use their powers on behalf of the summoner from astral space.