I personally have a very positive outlook on the new system. Allowing me to hone, or grow into, a specialization/class based on the skills I choose to develop feels a lot more freeing to me personally, rather than picking a class/specialization on the outset.
I don't see how this limits anyone's ability to roleplay as this just makes ability access (or lack thereof) more self-imposed rather than being decided by the game. I'm sure there will be lore reasons as to why you can do so, if you need some kind of embedded justification. You probably won't be able to be all powerful by just playing through a single campaign. Even if you can, it's still up to you to decide to actually make your character that way. Overall, as far as I remember, your character class never had much of an impact on how you interacted with the world other than combat in the Mass Effect franchise anyway. I'm all for options and build variety.
Lastly, new mechanic of allowing the player to switch specializations on the fly might actually prove more positive when it comes to the usefulness of your companions in combat. Because my class was determined at the start, there was a set group of companions that would be the most useful in combat scenarios. Now, you have the option to take whichever companions with you and adjust your class accordingly.
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