The extra 2 HP per hit dice on summons actually is totally useless now (with few -POSSIBLE?- exceptions, such as Giant Insect and Summon Fey but if I'm wrong please enlighten me. 

•  a 3 HP Owl familiar isn't bad, I actually like that, but no more ridiculous board control with many geese for the DM to handle. 
• Giant Insect and Summon Fey would gain from the magical attacks, or perhaps they're innately magical already? Not sure here. This means my find familiar attacks are magical, but it is a goodberry ferry and scout more than anything. 
• Would the +2 HP per hit dice even function on Summon Fey because it doens't list hit dice as the HP is determined by the spell level. I'm confused on how this works. Do I now treat spell level as the hit dice for the extra 2hp? Please advise. I guess Giant Insect too. 
• My spirit class feature is very strong, and I like that, but there is no longer any use (besides a bolstered familiar) for the Mighty Summoner class feature.

Perhaps if we changed Mighty Summoner to:

At 6th level, beasts and fey that you conjure are more resilient than normal. Any beast or fey summoned or created by a spell that you cast gains two benefits:

• The creature appears with more hit points than normal: extra hit points equal to your druid level. The damage from its natural weapons is considered magical for the purpose of overcoming immunity and resistance to nonmagical attacks and damage. Additionally, when a creature is damaged by the effects of your conjure animals or conjure woodland beings they take additional damage equal to your wisdom modifier. 

As I chose to make the switch to DND ONE for the campaign I play this druid in, I want to be able to work with my DM to come up with some kind of a solution since I can't summon many beasts or fey with actual stat blocks anymore. The Bear spirit needs work too, which was pointed out to me by my DM. She's going to allow me to stack the THP from Bear Spirit with the wild shape THP.

This is probably too strong, but I like this:

Bear Spirit. The bear spirit grants you and your allies its might and endurance. Each creature of your choice in the aura when the spirit appears gains additional hit points added to their hit point maximum equal to your druid level. In addition, you and your allies gain advantage on Strength checks and Strength saving throws while in the aura.

Guardian Spirit. Beginning at 10th level, your Spirit Totem safeguards the beasts and fey that you call forth with your magic. When a beast or fey that you summoned or created with a spell ends its turn in your Spirit Totem aura, that creature regains a number of hit points equal to half your druid level. Additionally, you and your allies inside the spirit's aura gain an additional buff: Bear: +1 AC Hawk: +1 Skill Checks Unicorn: +1 Saving Throws

This subclass is the (only?) one that does not work at all with the new rules.  Treantmonk did a video on the problem and how to solve it.  Hope this helps.

https://www.youtube.com/watch?v=CHvViD86JhI

Yes, shepherd Druid is broken under the new rules. If you want to play one I would suggest playing them under the 2014 rules. We will have to wait until it gets updated in a future book.  

Well, I certainly am going to miss my flocks of birds and packs of panthers, but I understand how it makes the game much more enjoyable for those not managing multiple attack rolls and hp pools. I think though, the FLAVOR of the shepherd has been lost in terms of spellcasting. 

Honestly, they could come up with something along the lines of bolstering the totem spirits instead of what I suggested. If they worked sort of like a spiritual weapon, gaining an attack, that'd be fine by me too. 

Revised Circle of the Shepherd Subclass:

Speech of the Woods (Starting feature): You gain the ability to converse with beasts and many fey. You learn Sylvan, if you already know Sylvan you learn another language of your choice. You may cast Speak With Animals at will.

Spirit Totem (Starting feature): You can call forth nature spirits to influence the world around you. As a bonus action, you can expend a use of your Wild Shape feature to magically summon an incorporeal spirit to a point you can see within 60 feet of you. The spirit creates an aura in a 30-foot radius around that point. It counts as neither a creature nor an object, though it has the spectral appearance of the creature it represents. As a bonus action, you can move the spirit up to 60 feet to a point you can see. The spirit persists for 1 minute or until you’re incapacitated or use this feature again. The effect of the spirit’s aura depends on the type of spirit you summon from the options below. Bear Spirit. The bear spirit grants you and your allies its might and endurance. As a reaction when a creature in your aura ends its turn, you may grant them temporary hit points equal to 5+ your druid level. In addition, you and your allies gain advantage on Strength checks and Strength saving throws while in the aura. Hawk Spirit. The hawk spirit is a consummate hunter, aiding you and your allies with its keen sight. As a reaction when a creature in your aura makes an attack, you may grant them advantage on that attack and any attacks they make until the start of your next turn. In addition, you and your allies have advantage on Wisdom (Perception) checks while in the aura. Unicorn Spirit. The unicorn spirit lends its protection to those nearby. As a reaction when a creature in your aura recovers hit points, you may increase the number of hit points regained equal to 5+ your druid level. In addition, you and your allies gain advantage on all ability checks made to detect creatures in the spirit’s aura.

Mighty Summoner Starting at 6th level, beasts and fey that you summon are more resilient than normal. When you use a spell to summon a beast or fey they gain the following benefits: The creature appears with more hit points than normal: 5 extra hit points per level of the spell that summoned it. The creature may deal its normal damage type with its attacks, or force damage. You make this choice each time the creature hits with an attack.

Guardian Spirit Beginning at 10th level, your Spirit Totem safeguards the beasts and fey that you call forth with your magic. At the end of your turn, choose a beast or fey that you summoned or created with a spell in your Spirit Totem aura, that creature regains a number of hit points equal to your druid level. Faithful Summons Starting at 14th level, the nature spirits you commune with protect you when you are the most defenseless. If you are reduced to 0 hit points or are incapacitated against your will, you can immediately gain the benefits of summon beast as if it were cast using a 9th-level spell slot. The summoned beast appears within 20 feet of you. If it receives no commands from you, it protects you from harm and attacks your foes. The spell lasts for 1 hour, requiring no concentration, or until you dismiss it (no action required).

This is what Treantmonk's Temple posted in the comments to their youtube video, as pointed out by my DM. These are pretty solid and I think we'll be doing this, but I do like brainstorming and discussing things here and seeing what other thoughts folks had.